The dynamics of the Citellophilus tesquorum altaicus (Ioff, 1936) number in the Kargy river valley during 1964–2013 have been analised. A close positive correlation between changes in the indices of abundance of this species on ground squirrels, in the burrows entrances and nests of the ground squirrels with ambient temperature change during this period and negative – with the amount of precipitation in September have been revealed. The 2.5 and 5.3 year periods have been found in the dynamics of the average annual index of the flea abundance on the animals. Probably the species numbers increase because of the development of more than one generation of fleas during the year owing to climate aridization.