A two year study was carried out from January 2012 to December 2013 on prevalence and pathology of mono infection of nematode Heterakis gallinarum and its co-infection with a protozoan parasite Histomonas meleagridis. For the study a sample size of 478 domestic chicken (Gallus g. domesticus L., 1758), 243 males and 235 females, weighing between 1 - 2.5 kgs collected from the different localities covering almost entire Kashmir valley were selected. The study revealed that prevalence rate of Heterakis gallinarum for 1st Year of study (2012) was 3.43% (8/233) and for the 2nd Year (2013) it was 5.3 % (13/245) giving an overall prevalence rate for two year study (Jan 2012 to Dec 2013) to be 4.39% (21/478). Range of intensity of worms was found to be 02 – 55 with Mean intensity of infection observed to be 20 ± 2.1. Faecal Egg Count was found to be very low i.e. <40 eggs per gram of faeces. On the other hand only two cases of Heterakis gallinarum co-infection with Histomonas meleagridis were reported, one in September 2012 and other in August 2013 giving overall prevalence of co-infection to be only 0.42% (2/478) and mean intensity of infection of Heterakis gallinarum during co-infection with Histomonas meleagridis was comparatively lower (07± 2). Gross lesions were seen on the ceca and liver only during co-infection of Heterakis gallinarum with Histomonas meleagridis and not during mono-infection of Heterakis gallinarum. Histological findings in the caeca during mono-infection revealed presence of adult worms in the lumen of intestine along with cellular debri and the infected tissue revealed intense chronic diffuse inflammatory processes with mononuclear and polymorphonuclear (heterophils) leucocyte infiltrations extending up to submucosa. During co-infection, histological studies of the infected livers revealed extensive infiltration of lymphocytes, mononuclear cells and scarce heterophills. Hepatocytes towards the periphery of the lesions contained punched out ovoid bodies which stained positive and became visible with PAS (Periodic Acid Schiff) stain. Microscopic examination of cecal lesions during co-infection showed hyperemia, ulceration and infiltration of heterophils, lymphocytes and macrophages extending from mucosa to the muscular layer. There was sloughing off of the epithelium and lumen was packed with fibrin, red blood cells and tissue debris.