The present study was conducted to envisage the epidemiology, clinicopathology and diagnosis of Ascites Syndrome (AS) in the poultry population of Mizoram. Detailed post-mortem examination was carried out in total of 129 dead birds from 17 different broiler farms located in different parts of Mizoram. Ascites syndrome was diagnosed in total 115 dead bids from 15 different broiler farms. The affected birds (3-5 weeks) showed distended abdomen, palpable fluid in the abdomen, redness of abdominal skin and depressed with loss of feathers. Often, apparently healthy birds found suddenly dead in affected farms. Post-mortem examination revealed dark musculature, distended abdomen with presence of clear to yellow colour fluid with or without fibrin clots, atrophied liver with rounding of edges and severe dilatation and hypertrophy of right ventricle of the heart. The other visceral organs like lungs, kidneys, spleen and intestine were found severely oedematous and congested. Microscopic lesions revealed disorganized and degenerated myofibrils with lack of cross striations in myocardium. Inter parabronchiolar septae were thickened with narrowing of parabronchiolar lumen due to severe congestion and oedema of lung parenchyma. Liver, kidneys and spleen showed mild to severe congestion, vacuolar degeneration with necrosis. Ascites syndrome found to cause high mortality in broiler population of Mizoram during the period from November to December of the year.