Provided is an olivine-type lithium iron phosphate having a composition represented by Formula I, comprising 0.1 to 5% by weight of Li3PO4, and comprising no Li2CO3 or, if present, comprising Li2CO3 in an amount less than 0.25% by weight: Li1+aFe1−xMx(PO4−b)Xb (I) wherein M, X, a, x and b are as defined above.The lithium iron phosphate comprises no lithium carbonate (Li2CO3) or, if present, comprises the Li2CO3 in an extremely small amount, and comprises Li3PO4 having superior electrochemical stability, thermal stability and ionic conductivity, thus advantageously imparting high-temperature and storage stability as well as stability and rate properties to lithium secondary batteries, when used as a cathode active material for the lithium secondary batteries.