A phospholipid derivative represented by the following formula (1): wherein [PG]k represents a residue of polyglycerin having a polymerization degree of k, wherein k is 2 to 50, R1CO and R2CO independently represent an acyl group having 8 to 22 carbon atoms, symbol "a" independently represents an integer of 0 to 5, symbol "b" independently represents 0 or 1, M represents hydrogen atom, an alkali metal atom, an ammonium, or an organic ammonium, and k1, k2, and k3 represent numbers satisfying the following conditions: 1 ≦ k1 ≦ (k+2)/2, 0 ≦ k2, and k1 + k2 + k3 = k + 2. The phospholipid derivative is highly safe for living bodies and can be suitably utilized in drug delivery systems such as liposome, and the like.
