The invention provides a method of producing a cathode active material for a lithium secondary battery, whereby it is possible to configure a lithium secondary battery in which the discharge capacity is improved and elution of lithium ions from the lithium metal phosphate is suppressed when washing the lithium metal phosphate after the same was synthesized. The method of producing a cathode active material for a lithium secondary battery includes synthesizing a lithium metal phosphate represented by a composition formula LiMPO4, wherein the element M represents one or two or more of transition metals selected from among Fe, Mn, Co and Ni, and after the synthesis, washing the lithium metal phosphate with a washing liquid containing lithium ion.