A complete random design experiment was conducted to determine the effect of arsanilic acid in wine diets on fresh waste production and composition and on decomposition of the waste stored in anaerobic pits. Vitamin and mineral fortified corn-soybean meal diets with 0, 100, or 200 ppm arsanilic acid were fed to growing-finishing pigs (14 to 91 kg) in winter and summer trials with daily fresh waste collection and addition to anaerobic pits. Average daily total waste production (wet basis) per pig, including hair, dust, wasted feed, waste water and excreta, was 3.8 kg during the winter trial and 4.8 kg during the summer trial. Average elemental arsenic excretion ranged from 35.7 mg to 62.8 mg per head per day. Arsenic concentrations (wet basis) in the anaerobic waste from pigs fed the 0, 100 and 200 ppm arsanilic acid diets for both trials were 0.54, 6.29, and 11.23 ppm, respectively. The presence of arsanilic acid in swine diets did not affect fresh waste production or composition. Arsanilic acid did enhance the decomposition of waste as shown by the reduction of dry matter and volatile solids in waste from arsanilic acid fed pigs. Dry matter content was reduced more than 60% in each trial in anaerobically stored waste from pigs fed arsanilic acid, while the dry matter content was reduced 23% and 39% in the waste from pigs fed the control diet. The presence of arsenic in the waste resulted in the retention of more total nitrogen (dry basis) and nitrogen in the ammonium form compared to waste with no arsenic but did not affect phosphorous, potassium and nitrate nitrogen levels.