Phytosterols are natural active substances widely found in plants and play an important role in hypolipidemia, antioxidants, antitumor, immunomodulation, plant growth, and development. In this study, phytosterols were extracted and identified from the seed embryos of 244 maize inbred lines. Based on this, a genome-wide association study (GWAS) was used to predict the possible candidate genes responsible for phytosterol content; 9 SNPs and 32 candidate genes were detected, andZmSCYL2was identified to be associated with phytosterol accumulation. We initially confirmed its functions in transgenicArabidopsisand found that mutation ofZmSCYL2resulted in slow plant growth and a significant reduction in sterol content, while overexpression ofZmSCYL2accelerated plant growth and significantly increased sterol content. These results were further confirmed in transgenic tobacco and suggest thatZmSCYL2was closely related to plant growth; overexpression ofZmSCYL2not only facilitated plant growth and development but also promoted the accumulation of phytosterols.