The hexane (PLH), ethyl acetate (PLE) and methanol (PLM) extracts of dried whole plant parts of Polygonum lanatum Roxb. (Family, Polygonaceae) obtained by successive cold extraction, were subjected to evaluate anti-inflammatory, analgesic and diuretic activity in experimental animals. Oral administration of either PLH and PLM at a dose of 300 mg/kg body weight showed statistically significant (p < 0.001) inhibition of rat paw edema by 41.09% and 30.15%, respectively, which was comparable to that of standard drug phenylbutazone (42.15%). Compared to the inhibition of acetic acid-induced writhing by aminopyrine (69.94%, p < 0.001), treatment with either PLH, PLE or PLM elicited significant inhibition of acetic acid-induced writhing reflex by 44.80% (p < 0.001), 33.87% (p < 0.01) and 62.29% (p < 0.001), respectively. In addition, mild to potent diuretic activity was observed after oral administration of these extracts in Swiss albino mice.