The paper deals with possibilities of maintenance optimisation of k-out-of-n systems. The first part of the paper briefly analyses influence of preventive maintenance concept on reliability of k-out-of-n system and presents possibilities of preventive maintenance optimisation with respect to maintenance costs. The second part of the paper presents a suggested method of maintenance optimisation in the case of a processing machine for dosing tiny loose material and smaller piece goods. The method takes into account not only maintenance costs but also production losses caused by a prospective failure of the system. The proposed method facilitates decisions on maintenance intervals modification and the range of maintenance from the economic point of view.