In order to explore the genetic mechanism of grain length in rice, one hundred and thirty recombinant inbred lines (RILs) derived from a cross between Milyang 46 and FJCD, and its linkage map including 119 molecular markers were used to map QTL controlling grain length in Wuyishan and Putian of Fujian Province, respectively. A total of 16 additive QTLs containing 7 from Wuyishan and 9 from Putian were identified on chromosomes 1, 2, 4, 5, 6, 7, 10, 11 and 12. Two QTLs were detected under two environments. The contribution rates for phenotype variance of qGL-4-6 were 5.69% in Wuyishan and 3.58% in Putian. The contribution rates for phenotype variance of qGL-10-1 were 15.82% in Wuyishan and 8.06% in Putian. Of 16 additive QTLs, qGL-5-3 and qGL-10-1 had significant additive × environment interaction effects, while contribution rates for phenotype variance from GE interaction effects were approximately zero.