From 1987 to 1990,the distribution and the population size of argali sheep(Ovis ammon) were investigated in Tibet. 99 sheeps were detected in a line transect sampling of 1550 km.From these data,the density of the sheep was estimated as 0.0820±0.0097 sheeps/km2 and it varied from 0.0121 to 0.3671 sheeps/km2,by using the Fourier Series Model as a detected function.The population size was about 8630±1021 individuals in about 105 302 km2 habitat of Tibet.The flock of the sheep was consisted of 5～6 sheeps.