S eed number is an important part of seed yield. Seed number regulation is a complex process and affected by different signals.Our research work focus on the organ (seed or seed precursor) initiation and the maximal possibility of seed number. In some dicot plants, like Arabidopsis, seed number depends on seed number per fruit (mainly on ovule number) and fruit number. Our previous work illustrated that Brassinosteroid (BR) positive regulated ovule/seed number through influencing the expression of downstream genes related to ovule early development by BR-induced transcription factor BZR1. bzr1-1D (P234L, gain-of-function mutant of BZR1) has enhanced BZR1 protein activity, placenta size and ovule/seed number per flower/silique. Soybean is an important dicot crop producing protein and edible oil. Phylogenetic analysis reveals BZR1-like genes are highly conserved in angiosperm and there are 4 orthologues in soybean (GmBZL1-4). The functional characterization of GmBZL2 illustrates that GmBZL2216L (P216L, conserved with P234L in Arabidopsis) enhances GmBZL2protein activityand increasesArabidopsis BR signaling and seed number, further demonstrating the conserved function and regulatory mechanism of GmBZL2. Overexpression of GmBZL2216Lin soybean enhances seed number, indicatingthepotential application of BR in seed yield of dicot crops. In monocot plants, like rice, seed (grain) number determines by grain number per panicle (mainly by panicle development and branch/spikelet number) and panicle number. Our results illustrates that BR regulates grain number through influencing BR-regulated transcription factors.For example,OsGATA7 modulated BR-mediated growth regulation and influencedrice architecture and grain shape/weight/number/yield. Although seed number regulation in Arabidopsis and rice has different mechanism, there are at least two common ways of BR regulation of seed number: non-specific increasing reproductive meristem size and specificinfluencing downstream related genes transcription.