Amidst global population growth and limited arable land， increasing crop yield per unit area is a key agricultural priority. Rice tiller number， a critical determinant of effective panicle number and yield， directly impacts food security. In this study， we isolated a less tiller number mutant， ltn4-1， from the japonica cultivar Shennong 9816 using EMS mutagenesis. Map-based cloning localized the candidate gene to a 106 kb interval on chromosome 5 between markers G5-10A2a and SN5-1. Compared with wild type， ltn4-1 exhibited reduced tiller number， widened leaves with bulged veins， and significantly increased numbers of large and inter-large small vascular bundles in flag， second， and third leaves. The mutant also showed enlarged cell size and increased cell number around vascular bundles. Agronomic evaluation revealed significant reductions in tiller number and grain weight per panicle. Transcriptome and qRT-PCR analyses identified differential expression of 14 known genes （including THIS1） involved in leaf width and tiller number regulation. Collectively， this study provides morphological， cytological， and transcriptomic characterization of ltn4-1， laying a foundation for cloning LTN4 and elucidating its molecular role in tiller number regulation in rice.