In a method of producing a positive active material for a lithium battery, a compound represented by the chemical formula H.sub.x Li.sub.y MO.sub.2 in a solution containing lithium ions is chemically oxidized, where 0.ltoreq.x.ltoreq.2, 0.ltoreq.y.ltoreq.2, 1<(x+y).ltoreq.2, and M is one or two kinds of transition metals selected from Co and Ni.