Investigating the efficiency and quality of serves in volleyball is carried out within the framework of the developed approach, which is based on mathematical treatment of the data of pedagogical observations after the game using the probability theory. Possibilities of this method are demonstrated at estimating the efficiency and quality of power serves in a jump and the aiming serves at the different moments of game, using the corresponding statistics of games in the national championship among the male teams of the super league. The downward tendency of the efficiency of power serves in a jump in each subsequent set is revealed.