Recent studies suggest that complex interacting processes are driving global amphibian declines. Increased ultraviolet B (UVB) radiation in the solar spectrum associated with ozone depletion has been implicated in declines, and evidence suggests that the effects of UVB radiation on amphibians may be greater at cooler temperatures. We tested the thermal sensitivity of UVB effects on amphibians in a controlled factorial experiment using the striped marsh frog, Limnodynastes peronii as a model species. We compared survival, growth and locomotor performance of embryonic and larval L. peronii reared under low and high UVB exposures at both 20 and 30 °C. Embryonic and larval L. peronii proved extremely sensitive to UVB damage and exhibited greater sensitivity at 20 °C compared with 30 °C. Embryonic survival to Gosner stage 25 was unaffected by UVB exposure at 30 °C, but at 20 °C survival was reduced to 52% under high UVB. Larval survival exhibited a similar trend. At 20 °C, all tadpoles survived under low UVB, whereas under high UVB there was 100% mortality after 15 days of exposure. At 30 °C, 86% survived under low UVB, but only 46% survived under high UVB. Sublethal effects such as, embryonic malformation, retarded larval growth and reduced larval swimming performance were also greater at 20 °C compared with 30 °C. Our results strongly indicate that UVB damage in amphibians is markedly increased at cooler temperatures. Thus, populations of UVB sensitive species occurring at cold climates may be at greater risk of declines due to increased solar UVB radiation.