Both Pinus yunnanensis and P. kesiya var. langbianensis are the main components of forest vegetation in central Yunnan and southern Yunnan, respectively. Previous studies have found that these two species may be differentiated from a common ancestor due to differences in precipitation in their respective habitats. To confirm the possible reasons for the differentiation of the two species in southwest China, we studied the seed germination of P. yunnanensis and P. kesiya var. langbianensis under different temperatures, water potentials and storage conditions. The temperature range of 15 degrees C to 30 degrees C was appropriate for seed germination and normal seedling emergence of the two pines. Under the water potential of 0 MPa to -0.6 MPa, germination percentages of P. yunnanensis and P. kesiya var. langbianensis were 63.2% to 80.8% and 71.2% to 91.6%, respectively. When the water potential decreased to -0.8 MPa to -1 MPa, the germination percentages of the two species decreased below 30%, but the germination percentage of P. yunnanensis was higher than that of P. kesiya var. langbianensis. After stored for 1, 3, 5 and 7 months at -20, 4, 15 and 25 degrees C, the seed germination percentages of the two species still maintained above 60%. When the seeds of P. yunnanensis and P. kesiya var. langbianensis were buried at Xishuangbanna in southern Yunnan, China, they lost vigor rapidly due to the highest precipitation. Especially, after buried for 2 months, the germination percentage of P. yunnanensis was 0. These results suggested that moisture is a key factor affecting seed germination of P. yunnanensis and P. kesiya var. langbianensis, and the seeds of P. yunnanensis preferred lower moisture levels for germination than P. kesiya var. langbianensis. Thus, the difference in the response of seed germination and storage of the two species to moisture levels may be an important factor causing the difference in their geographical distribution patterns.