Anti-inflammatory factor (AIF) is a water soluble extract of three herbs, Panax notoginseng (Burk.) F. H. Chen, Rehmannia glutinosa Libosch and Eleutherococcus senticosus. The present study aimed to investigate the safety and efficacy of herb extracts, AIF, on Korean knee osteoarthritis patients for six weeks. Fifty seven patients with knee osteoarthritis, ranging from 43 to 73 years of age, who fulfilled the "American College of Rheumatology" (ACR) classification of idiopathic osteoarthritis of knee and radiographic criteria were randomly selected and enrolled for the study. After initial screening and resting period, two capsules each of AIF (Each capsule contains; 400 mg) and similar identical placebo were administered twice a day to both groups. Pain intensity at second, fourth, and sixth weeks of study as well as one week after discontinuation of drugs was assessed by using 100 mm visual analogue scale (VAS). Changes in the Korean version of the Western Ontario and McMaster Universities (K-WOMAC) index score were compared at the initiation and completion of the study. VAS assessed by patients were significantly reduced (at visit 2; 54.64+/-14.72, at visit 4, 37.32+/-16.58, p< 0.001) after AIF administration. Results showed an improvement in the physical function of K-WOMAC scale which was significantly higher (p=0.013) in AIF than placebo group, and decreases of total K-WOMAC score were also significantly higher (p=0.030) in AIF groups than placebo group. No serious adverse effect was observed, and there was no difference in incidence of adverse effect between AIF and placebo groups. In this population of Korean patients with knee osteoarthritis, AIF was found to be safe, tolerable and effective for symptomatic improvement of pain and physical function.