The objective of this study was to investigate the variation of HSP70 mRNA level in dairy cows and relationships of its closely linked microsatellite loci with heat tolerance traits. Blood samples were collected from ten healthy Holstein cows with the same age and milking stage at different temperatures-humid-index (THI) (86.2, high temperature; 70.9, critical high temperature, and 56.8, optimum temperature). The mRNA levels of HSP70 of lymphocytes in peripheral blood were analyzed using real-time RT-PCR. The mRNA level of HSP70 was increased with the THI; the mRNA level of HSP70 at high temperature was higher than others (P<0.01). This indicated that the bovine HSP70 gene may act as a potential can-didate gene for response to heat shock. Genetic variation of three microsatellite loci BMS468, BM1258, and BM1815, which were closely linked to HSP70 gene on chromosome 23, was analyzed in 160 Holstein cows with non-denaturing poly-acrylamide gel electrophoresis. The association between these microsatellite loci and heat tolerance traits were analyzed by least square linear model. The results showed that 134 bp/128 bp at BMS468 and 186 bp/148 bp at BM1815 were the most favorable genotypes for HTC, red cell potassium, and decrement rate of milk yield in high temperature (P<0.05); 101 bp/99 bp at BM1258 was the most favorable genotype for decrement rate of milk yield in high temperature (P<0.05).