This study aimed to examine the anti-inflammatory properties of boric acid (BA) in treating knee osteoarthritis (KOA) in rats, evaluating its biochemical and histopathological therapeutic effects. A KOA rat model was induced by injecting monosodium iodoacetate into the knee joint. Random assignment was performed for the experimental groups as follows: group-1(control), group-2(KOA control), group-3 (BA:4 mg/kg, orally), group-4(BA:10 mg/kg, orally), group-5(BA:4 mg/kg, intra-articularly), and group-6(BA:10 mg/kg, intra-articularly). The rats received 100 µL of BA intra-articularly on days 1, 7, 14, and 21 or 1 mL orally once a day (5 days/week) for 4 weeks. Serum levels of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and activity of matrix metalloproteinase-13 (MMP-13) were measured. Histopathological and immunohistochemical analyses were performed on knee joint samples using specific antibodies for IL-1β, TNF-α, MMP-13, and nitric oxide synthase-2 (NOS-2). Group-2 exhibited higher serum IL-1β and TNF-α levels and MMP-13 activity than group-1 (P < 0.05). However, IL-1β and TNF-α levels and MMP-13 activity were lower in all treatment groups than in group-2, with statistically significant reductions observed in groups-4, 5, and 6. Histopathologically, group-2 displayed joint space narrowing, cartilage degeneration, and deep fissures. Groups-5 and 6 demonstrated significant joint space enlargement, articular cartilage tissue regeneration, and immunostaining patterns similar to those in group-1. Immunohistochemically, group-2 showed significant increases in IL-1β, TNF-α, MMP-13, and NOS-2 expression. However, all treatment groups exhibited reductions in these expression levels compared to group-2, with statistically significant decreases observed in groups-5 and 6 (P < 0.01). BA shows potential efficacy in reducing inflammation in experimental KOA model in rats. It may be a promising therapeutic agent for KOA, warranting further clinical studies for validation.