Oryza sativa SPL14 (OsSPL14), identified as the IDEAL PLANT ARCHITECTURE1 or WEALTHY FARMER’S PANICLE gene, plays a critical role in regulating rice plant architecture. Here, OsSPL14-overexpression transgenic rice plants had shorter growth periods, short narrow flag leaves, and thick green leaves compared with wild type ‘MH86’ plants (WT). Additionally, transgenic lines had higher chlorophyll a (Chl a), chlorophyll b (Chl b), and carotenoid (Car x) contents at both seedling and mature stages. Expression of OsSPL14 increased at transcriptional level, and OsSPL14 protein level was substantially increased in transgenic lines relative to WT. A transcriptome analysis identified 473 up-regulated and 103 down-regulated genes in the transgenic plants. The expression of differentially expressed genes (DEGs) involved in carotenoid biosynthesis, abscisic acid (ABA) metabolism, and lignin biosynthesis increased significantly. Most of DEGs participated in “plant hormone signal transduction” and “starch and sucrose metabolism” were also up-regulated in the transgenic plants. In addition, there were higher ABA and gibberellin acid 3 (GA3) levels in OsSPL14-overexpression rice plants at seedling and tillering stages compared with WT. In contrast with that of WT, lignin and cellulose contents of culm increased distinctly. Also, silicon and potassium contents increased dramatically in transgenic lines. Meanwhile, the chalkiness ratios and chalkiness degrees decreased, and the gel consistency levels improved in transgenic lines. Thus, overexpression of OsSPL14 influenced growth period, leaf development, hormonal levels, culm composition, and grain quality characters of rice, which provides more insight into the function of OsSPL14.