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Brine from the saline Qarhan Lake was evaporated at 28±2°C in a clean environment. Two groups of experiments were conducted; one with complete separation of precipitate and brine at different stages of evaporation, and the other with continuous precipitation during the evaporation. Seventy-nine precipitate and brine samples were collected during the experiments, and the  37 Cl values were determined using an improved thermal ionization mass spectrometry procedure for precise measurement of chlorine isotopes based on Cs 2 Cl + ions. Based on the concentrations of Na + , K + , and Mg 2+ , evaporation was divided into three main precipitation stages as follows: halite dominant, carnallite dominant, and bischofite dominant. The  37 Cl solid and  37 Cl liquid values of the precipitate and coexisting brine samples at different stages showed the following characteristics. The precipitates were enriched with 37 Cl relative to the coexisting brine samples, and the  37 Cl of both the precipitate and brine samples decreased gradually during evaporation. The fractionation factors (α h ) between halite and brine were the highest, followed by that (α c ) between carnallite and brine, and then that (α b ) between bischofite and brine. The α c and α b values of less than one, which indicate the precipitate is enriched in 35 Cl, were found when the evaporation process entered a new stage. However, the δ 37 Cl values of carnallite, bischofite, and the coexisting brine samples decreased during evaporation. The residual brine is a 35 Cl reservoir. The experimental phenomena were consistent with the δ 37 Cl values in saline deposits in the literature.  37 Cl can be used as an indicator of brine evaporation processes, which is important in the exploration of sylvinite deposits. saline lake, brine, evaporation, chlorine stable isotope, fractionationCitation:Luo C G, Xiao Y K, Ma H Z, et al. Stable isotope fractionation of chlorine during evaporation of brine from a saline lake.