In order to study litter decomposition in Robinia pseudoacacia and Fraxinus velutina mixed forests with different ages in the Yellow River Delta, we selected 7 a, 12 a, 21 a and 30 a mixed forests to investigate litter decomposition characteristics by litter bag technique during two years. The results showed as following: (1)The decomposition coefficients of all mixed forests ranged from 0.44 to 0.60, and it followed the order of 30 a＞21 a＞12 a＞7 a; the half decomposition periods were 1.15～1.58 a and the decomposition periods were 4.96～6.83 a, and they followed the order of 7 a＞12 a＞21 a＞30 a; (2) Litter decomposition rate was significantly positively correlated with nitrogen content of litter, but negatively correlated with C/N ratio; there were significant differences in nitrogen content of litter among four mixed forests, and there was no significant difference in C/N ratio of litter between 12 and 21-year-old mixed forests, but the difference in this parameter between 7 and 30-year-old mixed forest was significant（p＜0.05）; (3) decomposition rate of litter was significantly positively correlated with soil organic matter and soil alkaline hydrolyzable nitrogen; there were significant differences in soil organic matter and alkaline hydrolyzable nitrogen among four mixed forests（p＜0.05）. These results suggested that with the increasing of forest age, the nitrogen content of litter increased, the C/N ratio decreased, and the litter decomposition rate accelerated.