The latitudinal species richness gradients of vascular epiphytes are positively correlated with high water availability. Zotz (2016) hypothesized that low temperatures and long-lasting frosts likely determine the latitudinal species richness gradients of vascular epiphytes; however, quantitative studies are limited. Here, we assessed epiphyte species richness along temperature and precipitation gradients in Japan covering cold-temperate to subtropical climates. We analyzed the relationship between the occurrence of 69 epiphytes (44 ferns, 24 orchids, and 1 ribes) and two climatic factors (precipitation of wettest month: BIO13 and temperature annual range: BIO7) using thin-plate spline and generalized additive models. The epiphyte species richness of all species, ferns, and orchids increased with increasing BIO13 in areas with temperatures under 32℃ of BIO7; however, this trend was unclear in areas with temperatures above 33℃ of BIO7. In Japan, 91.5% of areas with temperatures above 32.5℃ of BIO7 had less than 0℃ of the mean temperatures of the coldest quarter. Our results suggest that low temperatures, especially frosts, as well as water availability determine latitudinal epiphyte species richness in humid temperate regions.