Abstract: An incubation test was conducted to study the effects of the decomposition of poplar and trabeculate alder leaf litters with different mixed ratios and under different application ways on soil microbial biomass carbon (MBC) and nitrogen (MBN). The mixed ratio of the litters had significant effects on soil MBC and MBN. On the 30th day of incubation, soil MBC and MBN were significantly higher in the treatments with ≥50% of alder litter than in the treatment with poplar litter only and the control. On the 75th day of incubation, the soil MBC in the treatments with ≥40% of alder litter and the soil MBN in the treatments with ≥30% of alder litter were significantly greater than those in the treatment with poplar litter only and the control. After 135 days incubation, soil MBC and MBN were significant higher in the treatments with ≥20% and ≥40% of alder litter than in the treatment with poplar litter only and the control, respectively. There was no significant difference in the soil MBC/MBN between the treatments with different mixed ratios of poplar and alder leaf litters and the control. Overall, soil MBC/MBN increased during the early period of incubation and decreased in the later period, suggesting that soil microflora changed during the decomposition of the litters. In the whole incubation period, the application ways of the litters had lesser effects on the soil MBC, MBN, and MBC/MBN, indicating that the addition ways of the litters did not affect soil microflora.