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As typical glacial relics, most species of pikas are confined to either high latitudes or high altitudes of the Holarctic region _ Within their distribution ranges, the Great Himalaya and Tibetan Highland are outstanding by the concentration of many species. Seven among 12 species hitherto described from Palaearctics are recorded from this area, even though with no detailed information on the mode of their life. Moreover the possible vertical segregation of two species, Ochotona macrotis and O. roylei, was suggested by the 1921 Expedition to Mount Everest reconnoitred from the Tibetan side (Thomas and Hinton, 1922). This problem, however, has been left without further confirmation just for a half century, obviously due to various difficulties to make field surveys in this area. Stimulated by this supposed interspecific segregation, the author made a series of observations upon ethology, ecology and sociology of the two Himalayan pikas, large-eared pika, O. macrotis and Royle's pika, O. roylei, in Khumbu region from October 1969 to January 1970. Following the previous report on O. roylei observed in central Nepal (Kawamichi, 1968), the present paper deals with vertical segregation, daily activities and social pattern of the two species, especially of O. macrotis. Henceforth, the species are cited by specific names alone. Their full names are listed here