To examine the effect of 2-azahypoxanthine (AHX) on rice plant (Oryza sativa L. cv. Nipponbare) growth, we carried out pot and field experiments. AHX was applied at 50 μM for two weeks at four growth stages (transplanting, tillering, panicle formation and ripening stages) in the pot experiment, and 1 mM AHX at three stages [at rising of seedling in nursery boxes (seedling treatment), transplanting and panicle formation stages] in the field experiment. Both pot and field experiments showed a tendency toward increased panicle number (PN), culm length (CL) and plant dry weights with AHX treatments. Brown rice yields were also improved by AHX treatments, especially when applying at stages of tillering and panicle formation and seedling and transplanting during pot and field experiments, respectively. In the latter, yield increased drastically up to 18.7, 15.8, 9.6 and 5.8% of control. However, panicle length and 1000-grain weight were not affected by AHX application. These results suggested that AHX increased the brown rice yield through its effects on PN and/or CL.