Pinus sylvestris var. mongolica and Larix principis-rupprechtii are fast growing tree species and are resistant to both cold and drought. Both species are commonly used for the afforesting of the Loess Plateau. As pure plantations of P. sylvestris var. mongolica and L. principis-rupprechtii age, soil fertility declines, tree growth slows, and natural regeneration ceases. These changes affect the productivity and sustainable management of local forests. Mixed-species plantations may be an effective strategy for overcoming these problems. Knowledge about mixed-species leaf litter decomposition and its effect on soil properties is important for evaluating interspecific relationships and compatibility in mixed forests. In this laboratory study, leaf litter from P. sylvestris var. mongolica or L. principis-rupprechtii was mixed with leaf litter from other tree species after grinding and then put into soil from an unvegetated area, incubated them to decompose for 120 days, after that to determinate the number of soil microbes, activities of soil enzymes and nutrient content of soil, to analyze the effects of leaf litter from different tree species decomposition on soil properties and the interaction (interactive promotion or inhibitory effect) between the litters decomposition. This laboratory study consisted of two parts. In the first part, leaf litter from 12 tree species (including P. sylvestris var. mongolica or L. principis-rupprechtii) was separately mixed into unvegetated soil to decompose. The results showed that single-species leaf litter increased urease activity by 54%-110%, dehydrogenase activity by 85%-288%, phosphatase activity by 81%-301%, soil organic matter by 29%-55%, and available N by 12%-49%. Single-species leaf litter had mixed effects on available P and cation exchange capacity (CEC). In the second part of the study, leaf litter from 10 or 11 tree species was separately mixed with leaf litter from either P. sylvestris var. mongolica or L. principis-rupprechtii and then added to the soil. Principal component analysis indicated that P. sylvestris var. mongolica leaf litter was mixed with that of Betula platyphylla, Robinia pseudoacacia, Ulmus pumila, Caragana microphylla, or L. rincipis-rupprechtii separately showed interactive promotion effects on soil, but P. sylvestris var. mongolica leaf litter was mixed with that of Populus simonii, Hippophae rhamnoides, Amorpha fruticosa, Platycladus orientalis, or Quercus liaotungensis separately showed interactive inhibitory effects. All the same, L. principis-rupprechtii leaf litter was mixed with that of R. pseudoacacia, B. platyphylla, P. simonii, or A. fruticosa separately showed interactive promotion effects on soil, whereas L. principis-rupprechtii leaf litter was mixed with that of C. microphylla, P. orientalis, Q. liaotungensis, H. rhamnoides, Pinus tabulaeformis, or U. pumila separately showed interactive inhibitory effects.