BACKGROUND Pyungwi-san (PWS, Heii-san in Japanese) is a mixture of six herbs and is traditionally used in Northeast Asia (especially Korea and Japan) for the treatment of gastrointestinal disorder, such as dyspepsia and inappetance induced by gastric dilatation and gastrointestinal catarrh. OBJECTIVE Although PWS is a widely used herbal prescription in Korea and Japan, little information is available in the literature on the safety and toxicity of PWS. As part of a safety evaluation of PWS, the present study evaluated the potential genotoxicity of PWS using a standard battery of test. METHODS We prepared PWS using a water extraction method and simultaneously extracted three compounds from PWS using high performance liquid chromatography. The PWS extract that was obtained was assayed for genotoxicity using the standard three tests recommended by the Korea Food and Drug Administration. These tests included the bacterial reverse mutation test (Ames test), the chromosomal aberration test using China hamster lung cells, and the micronucleus test using ICR mice. RESULTS The Ames test showed that the PWS extract did not induce an increase in the number of revertant colonies compared with vehicle control at any dose in all of tester strains. In the micronucleus test, no significant increase was observed in micronucleated polychromatic erythrocytes (MNPCEs) at any dose of PWS extract compared with vehicle control. Conversely, chromosomal aberration test showed that the PWS extract at a dosage of 4500 μg/mL induced an increase in the number of chromosomal aberrations in the 6 h group with metabolic activation compared with the vehicle control. CONCLUSIONS PWS extract exhibits genotoxicity, based on the results of the chromosomal aberration test. Thus, further detailed experiments will be needed to identify the ingredient responsible for inducing this genotoxicity and to determine its mechanism.