Apolipoprotein C1 is a lipoprotein with a length of 57 amino acids normally found in plasma and responsible for the activation of esterified lechitin cholesterol with an important role in the exchange of esterified cholesterol between lipoproteins and in removal of cholesterol from tissues.

Its main function is inhibition of CETP, probably by altering the electric charge of HDL molecules. during fasting (like other apolipoprotein C) is found primarily within HDL, meanwhile after a meal it is found within the surface of other lipoproteins. in contrast when proteins rich in triglycerides like chylomicrons and VLDL are broken down this apoprotein is transferred again to the HDL.