In the present study,ajaponicarice(Oryza sativa L.)variety Nipponbare,an indicavariety 9311 and a set of chromosome segment substitution lines(CSSLs)which were generated using Nipponbare as the recipient parent and 9311 as the donor parent were used as the experimental materials.The CSSLs were grown in 2012(normal temperature condition)and 2013(high temperature condition)in Yangzhou,Jiangsu,and were used to map the quantitative trait loci(QTLs)for heat tolerance,based on the heat tolerance index[(The seed setting rate under normal temperature condition-The seed setting rate under high temperature condition)/The seed setting rate under normal temperature condition].As a result,three QTLs related to heat tolerance in rice were mapped on chromosomes 2,4and 12,respectively.They had LOD(logarithm of odds)scores of 2.56,4.02 and 2.79,and contribution rates of 4.95%,7.99%and 5.44%.Among them,qHT12.1showed positive effect,while qHT2.1and qHT4.1showed negative effect on heat tolerance.The results lay a foundation for the fine mapping and cloning of the QTLs and genes related to heat tolerance,and for the breeding of heat-tolerant rice varieties. In the present study, ajaponicarice (Oryza sativa L.) variety Nipponbare, an indica- avariety 9311 and a set of chromosome segment substitution lines (CSSLs) which were generated using Nipponbare as the recipient parent and 9311 as the donor parent were used as the experimental materials The CSSLs were grown in 2012 (normal temperature condition) and 2013 (high temperature condition) in Yangzhou, Jiangsu, and were used to map the quantitative trait loci (QTLs) for heat tolerance, based on the heat tolerance index [(The seed setting rate under normal temperature condition-The seed setting rate under high temperature condition] / The seed setting rate under normal temperature condition]. As a result, three QTLs related to heat tolerance in rice were mapped on chromosomes 2, 4 and 12, respectively. They had LOD (logarithm of odds) scores of 2.56, 4.02 and 2.79, and contribution rates of 4.95%, 7.99% and 5.44% .Among them, qHT12.1showed positive effect, while qHT2.1and qHT4.1showed negative effect on heat tolerance The resul ts lay a foundation for the fine mapping and cloning of the QTLs and genes related to heat tolerance, and for the breeding of heat-tolerant rice varieties.