Martyniškis is a village in Jonava District Municipality, in Kaunas County, Lithuania. Martyniškis lies at 70 m above sea level. It has 21 inhabitants (2021). The nearest city is Jonava, 9.6 km to the southeast. Among the landmarks around are Ninth Fort (30 km), M. K. Čiurlionis National Art Museum (33 km) and Beit Medrash Hagadol Synagogue (9.7 km). Among the natural features are Vainiai poplar (5.9 km).