A population of recombinant inbred lines derived from the cross between rice varieties Zhenshan 97 and Minghui 63 was examined for heading date in two plantings (winter in Hainan and summer in Wuhan) to analyze QTLs for heading date using an ultra-high density SNP linkage map.Comparison of the results from the short-day Hainan winter and long-day Wuhan summer revealed large differences of QTLs between the two conditions.The main QTL for heading date in long-day environment of Wuhan was detected near the centromere of chromosome 7,but its effect was not significant in Hainan short-day environment.In contrast a major QTL for heading date was detected in the region of 9.12-9.65 Mb on chromosome 6 in Hainan but its effect was not significant in Wuhan conditions.The results will be useful for understanding the genetic basis of rice flowering.