Increasing the breakdown of stored fat in adipose tissue leads to reducing fat content, enhancing feed efficiency and, consequently, decreasing the production cost of poultry. The processes of lipolysis are not completely understood, and the proteins involved in this process need to be identified. An adipose triglyceride lipase (ATGL), recently identified in several species, has not been studied in avian species. We have cloned the full-length coding sequences of ATGL cDNA for the chicken, turkey, and quail. Sequence comparisons among mammals and these avian species showed that the avian ATGL have 2 conserved domains, the patatin domain and the hydrophobic domain. The patatin domain contains lipase activity, and the hydrophobic domain exhibits lipid droplet binding. The high levels of chicken, turkey, and quail ATGL mRNA and protein are exclusively found in subcutaneous and abdominal adipose tissues. In addition, chicken ATGL (gATGL) is mainly expressed in the fractionated adipocytes compared with stromal-vascular cells that mostly contain preadipocytes (P < 0.001). Furthermore, ontogeny of gATGL mRNA and protein expression in adipose tissue showed induction of gATGL immediately after hatching before access to food (P < 0.05), suggesting that an energy deficit due to posthatching starvation may increase breakdown of stored fat via increasing gATGL expression in adipose tissue. Our studies showed that expression of the chicken ATGL is adipose specific and regulated developmentally, suggesting that a possible modulation of ATGL expression would regulate fat deposition in avian species.