The lipoprotein lipase (LPL) catalyzed hydrolysis of plasma lipoproteins is a rate-limiting step in the lipid transport into peripheral tissues. The aim of the present study was to isolate monoclonal antibodies against chicken adipose LPL and to investigate whether chronic infusion of the LPL monoclonal antibodies inhibits adipose LPL activity and consequently reduces fat accumulation in broiler chickens. The LPL catalyzed very low density lipoprotein (VLDL) hydrolysis was completely inhibited by the addition of 100 microg/mL of monoclonal antibodies (CLP10, CLP14, CLP16) in the in vitro incubation with plasma VLDL and LPL. A single injection of CLP10 and CLP16 into chickens fed or starved for 24 h elevated plasma triacylglycerol concentrations for 24 h, whereas that of CLP14 was ineffective. Intravenous injection every other day and continuous infusion by osmotic minipump with CLP16 maintained higher plasma triacylglycerol concentration for 5 d than that of the control group and extensively reduced LPL activity in adipose tissues and abdominal fat pad weight. Lipoprotein lipase mRNA and protein levels in adipose tissue were not modified by chronic administration of anti-LPL antibody. The results indicate that chronic administration of anti-LPL antibodies is effective in retarding fatness in broiler chickens, and the antibodies are a proper subject for studies of lipoprotein metabolism.