Sixty-six female patients diagnosed with knee osteoarthritis (OA) were randomized to receive Fennel extract (Foeniculum vulgare) or a placebo for knee pain. The outcomes of interest included the following: the Western Ontario and McMaster Universities Arthritis Index (WOMAC) questionnaire (in Farsi) total score and subscales for pain, stiffness, and physical function, as well as the pain on a Visual Analogue Scale (VAS). All outcomes were measured at baseline and at 2 weeks follow-up. Results revealed that the WOMAC subscale for pain (p=0.002), and physical function (p=0.006) scores were significantly in favour of the fennel group compared to the placebo group. Furthermore, the WOMAC total score was also significantly in favour of the fennel group (p=0.008). Finally, the VAS pain subscale was also statistically significantly lower in the fennel group (p=0.006) compared to the placebo.