Large number of well-filled grains per panicle is an important yield component trait in rice. A combination of QTL mapping and transcriptome profiling was used to identify candidate genes for grain number. A framework linkage map was constructed using 166 SSR markers evenly distributed over the 12 rice chromosomes. QTL mapping using 3 years phenotyping data on a set of recombinant inbred lines derived from a cross between Pusa 1266 (high grain number) and Pusa Basmati 1 (low grain number) identified one consistent QTL qGN4-1 on the long arm of chromosome 4 with major effect on grain number. This QTL was co-localized with major QTLs for primary and secondary branches per panicle, and number of panicles per plant. The QTL interval was narrowed down to 11.1 cM (0.78 Mbp) by targeted enrichment of the region with six additional markers. Microarray transcriptome profiling revealed eight genes in the qGN4-1 region differentially expressed between the two parents during early panicle development. Synteny of this QTL and potential candidates was examined in wheat, barley, maize, sorghum, and Brachypodium to further validate the association.