Transovarial transmission of a newly isolated large intraerythrocytic parasite, Babesia sp.1 by Haemaphysalis longicornis was experimentally demonstrated. Larvae of H. longicornis were transovarially infected with the parasite by feeding as adults on the calf which had been experimentally infected with B. sp.1. Piroplasms of B. sp.1 were observed in peripheral blood of the calf which was infested with the parasite-infected larvae. Based on the transmissibility of the parasite with vector ticks, this parasite was suggested to be a variety of B. ovata. Thus, we propose a new variety name for B. sp.1 as B. ovata oshimensis n. var.