Glutathione S-transferases (GSTs) are important drug-metabolizing enzymes that catalyze the binding of glutathione (GSH) to electrophilic substances. GST has genetic polymorphism, and the enzyme activity of GST affects the metabolism of certain drugs in vivo. In the present day, we investigated the GST enzyme activity and GSTA1 gene polymorphism in 170 patients with hematological diseases and explored their relationship. The GSTA1 gene polymorphism of the patient was analyzed by PCR- restriction fragment length polymorphism (PCR-RFLP) technique, and the base sequences of the four mutation sites (-631, -567, -69, and -52) in the promoter region were determined by DNA-Sequencer. The patient's GST enzyme activity was calculated by measuring the rate at which it catalyzed the reaction between 1-chloro-2,4-dinitrobenzene (CDNB) and GSH. The average GST enzyme activities of males and females were 5.20±0.13 and 5.17±0.12 nmol/min/mL, respectively, and the difference was not significant (P = 0.91). The frequencies of genotypes GSTA1*A*A (wild genotype), GSTA1*A*B (heterozygous genotype), and GSTA1*B*B (homozygous mutant genotype) were 75.3%, 22.9%, and 1.8%, respectively. Alleles GSTA1*A and *B were distributed at 86.8% and 13.2%, respectively. The genotype frequency distribution between males and females was no significant difference by Pearson’s chi-square test (P = 0.743). The average GST activity of the heterozygous mutant genotype (4.83±0.76 nmol/min/mL) was lower than the wild genotype (5.34±1.26 nmol/min/mL, P = 0.018), and higher than that of the homozygous mutant genotype (3.32±0.07 nmol/min/mL, P = 0.022). These findings might help us improve the individualized treatment of patients with hematological diseases in the future and promote the development of precision medicine for blood diseases.