In this study, two homogeneous chitin and chitosan hexamers and one partially acetylated chitosan hexamer were used to investigate the degree of acetylation (DA) effects of chitooligosaccharides on the growth and photosynthesis of wheat seedlings. Both chitin and chitosan hexamers showed a significant promoting effect on the growth and photosynthesis of wheat seedlings but the positive effect depended on their DA. The homogeneous chitosan hexamers [(GlcN)6] exhibited the optimal activity compared to other samples. Seven days after (GlcN)6 treatment, the growth parameters of wheat seedlings were all significantly enhanced including fresh mass, dry mass, and length of both shoots and roots, and the contents of soluble sugar were increased by 22.8%. Additionally, (GlcN)6 could significantly promote (by 90.0%) the photosynthetic rate of wheat seedlings. Both Rubisco and fructose-1,6-bisphosphatase activity of photosynthetic carbon metabolism was also found to be significantly improved by (GlcN)6 treatment.