Abstract: Introducing opaque-2 gene into normal maize germplasm by molecular assisted selection（MAS）was a popular technique in maize breeding nowadays. In this study，several near-isogenic lines developed by MAS were used to discuss the genetic effect of o2 gene. The results showed that introducing o2 gene into normal maize germplasm with different genetic background could improve lysine（which is called the first restrictive amino acid）and other amino acids contents significantly. 100-kernel weight decreased and 100-kernel volume increased slightly when o2 gene was introduced into tropical and subtropical maize germplasm. However，100-kernel weight and 100-kernel volume increased greatly when o2 gene was introduced into temperate germplasm. Introducing o2 gene into normal maize germplasm with different genetic background was a good way for germplasm enhancement in quality protein maize（QPM）.