The primary object of the invention is to provide a method of producing novel phosphate and potash (PK) containing compound fertilizers in the form of powders showing good handle-ability by which method the phosphate components contained in an incinerated ash residue of chicken droppings is improved in solubility and thus rendered effective or available and, at the same time, the free CaO-derived alkali is neutralized, as well as such novel phosphate and potash(PK) containing compound fertilizers. The above object can be accomplished by adding an alkaline earth metal compound to the powdery incinerated ash residue of chicken droppings, adding a mineral acid to the resulting mixture, allowing the reaction to proceed and raising the reaction system temperature by utilizing the heat of reaction of the powdery alkaline earth metal compound with the mineral acid to thereby promote the reaction between the free CaO contained in the incinerated ash residue of chicken droppings and so forth with the mineral acid and convert the phosphate components to citric acid-soluble P.sub.2O.sub.5 and, at the same time, maintaining the product neutral or weakly acidic.