Siberian Federal University

V.V.Chueshev has constructed a general theory of multiplicative (multi-valued) functions and Prym differentials on a compact Riemann surface. In this article we begin to construct the theory of Prym differentials on a finite Riemann surface. Explicit forms of all elementary Prym differentials for every characters are given.We find the dimensions of two important factor spaces of Prym differentials and the dimension of the first holomorphic de Rham cohomology group of Prym differentials for unessential characters. Moreover we give explicit bases in these factor spaces. We also give formulae for multiplicative functions and multiplicative units for every characters on finite Riemann surfaces. Keywords: multiplicative function, Prym differential