Grain yield variations in PSB Rc18, NSIC Rc222 (inbreds) and NSIC Rc202H (hybrid) were determined across growing environments as a function of cropping seasons and locations in rice producing areas in the Philippines. Contribution of location to variation in grain yield is 61.0%, while 12.7% for the season, and 6.1% for the genotype and this must be due location by season by genotype interactions. Dry season cropping in Nueva Ecija produced the highest mean grain yield. On the other hand, wet season cropping in Davao del Sur produced the least mean grain yield. The genotypes differed in their response to varying growing environments. NSIC Rc202H is the highest yielder among genotypes during dry season in Nueva Ecija. NSIC Rc222 is the most stable, having relatively high and constant grain yield across environments. High grain yield is associated with aboveground biomass particularly in NSIC Rc202H (R2 = 0.8615). Harvest index of NSIC Rc222 has less variations across growing environments, hence, one reason for its relative stability. Among yield components, spikelets per panicle and percent filled spikelets are highly correlated with grain yield (r = 0.85 and r = 0.82, respectively). Grain yield is highly influenced by solar radiation and temperature. Growing degree days (GDD) accumulated by genotypes are generally lower during wet season than dry season. While genotypes with different growth durations may require different GDDs, the higher the GDD accumulated by a particular genotype, regardless of growth duration resulted in higher grain yield, and variations in accumulated GDD is affected directly by temperature and indirectly by solar radiation, contributed to the variations in grain yield across growing environments.