In view of the continued screening of biological activities of seaweeds, Gracilaria dura (Ag.) J.Ag., the most common red seaweed species along Hare island, Thoothukudi in the south east coast of Tamil Nadu, India was identified to study the diuretic effect on mice. The plant materials were air dried, powdered and methanol extract at the dose of 200mg/kg and 400mg/kg body weight administered to mice. Methanol crude extract showed remarkable diuretic activity in both doses from 1 hour to 4 hour as compared to the standard drug furosemide by increasing the total urine output and increased excretion the total Sodium, Potassium and Chloride levels. The present study has been provided the confirmation for the diuretic activity of Gracilaria dura (Ag.) J.Ag. which could partly provided to its medicinal purposes also.