Abstract: We investigated nest-site characteristics and reproductive season changes of horned larks (Eremophila alpestris) and small skylarks (Alauda gulgula) during three periods from Apr.to Sep.in 2000-2002 at Haibei Alpine Meadow Ecosystem Research Station,the Chinese Academy of Sciences,in northern Qinghai Province.Nests of horned lark (n=27) and small skylark (n=43) were used to eximined nest-site characteristics.We used stable isotopes to determine the dietary contributions ratio of raise nestling,and compare nest-site characteristics and overlap degree of diet of horned lark and small skylark.The result shown:1)there was significantly difference between the exoteric degrees of nests in horned lark and small skylark (P<0.01),which were 92.16% and 34.61%,respectively.2)the number of distance to nearest structural element of horned lark (0.07±0.26) was significantly lower than that of small skylark (2.57±1.19)(P<0.01).3)the vegetation height and the percentage of vegetation cover of nest-site of small skylark were significantly higher than those of horned lark(P<0.01).4)the food resource,reproductive season length and reproductive frequency largely overlapped in these two species.There is a balance between cost and benefit of horned lark and small skylark in nest-site selection.It is possible that predation and thermal consideration have guided the evolution of nest-site selection of two species,and the coexistence mechanism of them is nest-site differentiation.