The dominant milk fat consists of neutral fat. The two main stages for synthesis of milk fat are: one the supply of fatty acids, and the other the incorporation of fatty acids with glyceroles. Malonyl CoA enables acetate to be converted into a long chain fatty acids. The related reaction is explained. By the mitochondria system of fatty acid synthesis, acetyl CoA reacts forming a long chain saturated or unsaturated fatty acids under anaerobic conditions in the presence of DPNH, TPNH, ATP and four kinds of enzymes explained. In the mammary gland of animal, all kinds of fatty acids can be synthesised. The systems related are assumed to be both mitochondrial and non-mitochondrial. Glucose has been approved as a precusor of glycerol. Its formation takes place in the mammary gland, mitochondria is more active in converting diglycerides to triglycerides than microsomes do. Blood triglycerides might be rearranged in the mammary gland. Morphological studies shows a whole picture of milk fat synthesis from its embryonic forms to its final globules which contain increased level of C4 to C14 acids.