Abstract: Commercial poultry has been kept in different flock sizes, so that an experiment designed in which 150 broilers were purchased, weighed initially and randomly divided into two groups A (50) and B (100) and were housed at poultry Experiment Station, Department of Poultry Husbandry, Tando Jam for 6 weeks. Broiler (A and B groups) were offered feed (iso-caloric and iso-nitrogenous) ad libitum and water 24 hours. Brooding temperature, humidity and vaccinations were provided as per recommendations. The results revealed that average total feed intake was significantly higher for larger flock size group B than small group A (3.781 and 3.717 kg b-1), respectively. Average live body weight of broiler increased significantly with the progress of period (P<0.01), while it was not different significantly for groups A (1.858 kg) and B (1.920 kg) per broiler, respectively. Mortality was higher for group B (4.0) than A (0.0) percent, respectively. Social behaviours show that aggression instigated and target was higher in A than B groups (4.2 vs 3.3 incidences 24 hr-1 b-1 P<0.01). Similar trends were noted for total aggression and social behaviour (P<0.01) respectively. Flying and playing behaviours in groups A and B were same (P>0.05). Feed Conversion Ratios in groups A and B were 2.242 and 2.202, while net profit earned was Rs. 10.113 and 12.075 per bird respectively. It was concluded that broiler housed in larger group sizes were resulted in better F. C. R and become more economical.