Abstract: This study focused on 44 elite individuals of Castanea mollissima Blume (Wangmo chestnut) and utilized a suite of analytical approaches—including genetic variation analysis, correlation analysis, principal component analysis (PCA), cluster analysis, and boxplot analysis—to investigate the diversity of their fruit phenotypic traits, encompassing 17 descriptive traits and 18 quantitative traits. Results showed that Wangmo chestnut involucres (spiny bracts) were predominantly ball-shaped with valvate dehiscence; most spine bundle colors were dark brown, reddish-brown was the most common nut color (41%), and ellipse was the dominant nut shape (59%). For the 17 descriptive traits, the diversity index ranged from 0.40 to 0.97, with pubescence density exhibiting the highest index (0.97) and level of hilum smoothing the lowest (0.40). For the 18 quantitative traits, the coefficient of variation (CV) spanned 6.69% to 39.95%, with variation magnitude (assessed by CV) ranking as follows: Kernel weight > total bur weight > seed weight > inner skin thickness > seed coat thickness > bur skin thickness > prickle width > nut thickness > prickle length > bur height > bur width > bur length > nut width > nut shape index > seed extraction rate > moisture content of nuts > nut height > kernel recovery rate; notably, traits including kernel recovery rate (6.69%), nut height (10.38%), nut shape index (14.48%), nut moisture content (11.33%), seed extraction rate (13.87%) and nut width (14.61%) had CVs < 15% (indicating relatively stable heredity), while all other quantitative traits had CVs > 15% (reflecting high dispersion and abundant variation among tested materials), and their genetic diversity indices ranged from 1.43 to 2.19. Correlation analysis revealed significant or highly significant associations among most quantitative traits: seed extraction rate exhibited a highly significant negative correlation with bur skin thickness (P<0.01) and a significant negative correlation with seed coat thickness (P<0.05); kernel recovery rate showed a significant positive correlation with total bur weight and bur height (P<0.05), a highly significant positive correlation with seed weight, nut width, nut thickness, nut height and kernel weight (P<0.01), and a significant negative correlation with seed coat thickness (P<0.05). However, nut moisture content showed no significant correlation with any other trait. Using an eigenvalue > 1 as the cutoff, five valid principal components (PCs) were extracted, with eigenvalues of 7.251, 2.468, 2.212, 1.363, and 1.149, and corresponding variance contribution rates of 40.282%, 13.710%, 12.288%, 7.572%, and 6.383%, respectively, yielding a cumulative variance contribution rate of 80.236%. Cluster analysis indicated that the 44 Wangmo chestnut resources could be divided into 3 major groups at a genetic distance of L=12, with varying degrees of phenotypic variation among groups: Group I was a small-fruited group, which were smaller in the weight of burs, seeds, and kernels; Group II was a large-fruited group characterized by higher mean values for most traits; Group III was a medium-fruited group featuring a low CVs in fruit shape index and high moisture content. Furthermore, boxplot analysis was performed on the three groups of Wangmo chestnut resources identified through cluster analysis. Among the traits evaluated, four indicators—seed extraction rate, kernel recovery rate, and moisture content of nuts—showed no significant differences, while the remaining 14 traits exhibited significant differentiation. Spine width in Group I and Group II exhibited outlier proportions of 11.54% and 11.11%, respectively. Furthermore, the seed extraction rate and moisture content of nuts in Group I, as well as the kernel recovery rate in Group II, showed a broad distribution range. Most indicators related to the size of the total bur and nut in Group III exhibited a significant upward distribution trend. This study elucidates the patterns of phenotypic diversity and characteristics of group differentiation in Wangmo chestnut germplasm, laying a solid foundation for the variety breeding of Wangmo chestnut.