A new rice (Oryza sativa L.) cultivar, ‘Oonari’, was developed to reduce the shattering habit of the high-yielding cultivar ‘Takanari’. To evaluate the effects of environment on its yield and related traits, Oonari and Takanari were grown in multiple environmental conditions at three locations in Japan. The whole and filled brown rice yields of Oonari were around 1000 g m−2, similar to those of Takanari. But the panicle number m−2 of Oonari was slightly but significantly higher than that of Takanari and the spikelet number per panicle was slightly but significantly lower. With respect to the effect of environment on yield of Oonari, cumulative radiation during 40 days after heading was positively related to whole brown rice yield of Oonari. Yield tended to be higher under increased atmospheric CO2 concentration than under ambient. Oonari was confirmed to exhibit high yield in various environmental conditions.