Objectives : To investigate the incidence of drug-induced liver injury (DILI) by combined-prescription of Korean herbal medicine (KHM; prescribed herbal medicine by doctors of traditional Korean medicine) and Western medicine on liver function. Methods : Sixty-nine in-patients who took KHM and Western medicine for various conditions were enrolled for prospective observational study. All subjects were given liver and renal function tests at the start of hospitalization to establish a baseline. After taking KHM and Western medicine, tests were done at approximately 4-week intervals afterwards. Results : Fifty-three subjects showed normal liver function test (LFT) at baseline, 50 subjects (72.5%) remained within the normal range at the second test, while 3 subjects (4.3%) tests revealed slight increase of LFT. However not a single patient had a high enough raised LFT to indicate liver injury. Sixteen of 69 subjects had abnormal baseline, 11 subjects recovered to normal levels and 5 subjects remained at abnormal level. Among all subjects, there was no statistically significant increase in LFT level between the first and second tests. Conclusions : This study shows that the combined-prescription of KHM and Western medicine did not cause any DILI. In some cases, combined treatment increased LFT levels but those increases were not high enough to have statistical significance. Additional large scale and systematical studies are required for more conclusive proof and results.