The study was undertaken to estimate the economic impact of gastrointestinal parasitic infections in sheep. A total of 117 Madras Red sheep selected in different age groups like >3 years, 2 years and 1 year were used in this study. Egg per gram (EPG) of faeces and body weights of the animals were measured in monthly interval from the year 2012- 2014 at an organised sheep farm, Post graduate research institute of animal sciences (PGRIAS), Tamil Nadu Veterinary and Animal Sciences University, Kattupakkam, Chennai, Tamil Nadu, India. The estimation of economic loss due to gastrointestinal parasitic infections was calculated by accounting the difference in mean body weight gain, dressing percentage of sheep (40%), cost of treatment per sheep and market price (Rs.400/Kg) of meat in Tamil Nadu. The faecal examination results revealed that all the animals were positive for gastrointestinal nematode infection over the period. On coproculture, Haemonchus contortus was found to be the predominant species. The regression analysis showed that for every unit of EPG increase there was 0.008 kg loss in weight gain, ceteris paribus. The total economic loss was calculated was Rs.1194/ animal in the group of EPG 501-1000 and Rs.1674/ animal in the group of EPG >1000. This study shows that the gastrointestinal nematodes contribute for loss of weight in sheep, its leads to income loss to the farmers. The controlling of GI nematodes and keeping the better deworming practices in sheep is very much essential for increase the farmers income.