Abstract: In this paper we establish the existence of single and multiple positi ve solutions to the periodic boundary value problems of second order singular n onlinear differential equations by means of positivity of Green’s function and the Krasnosel’skii fixed point theorem in c ones. The problem has at least one positive solution when nonlinear term f i s singular and sublinear, and the problem has at least two positive solution s when f is singular and superlinear. The paper generalizes and improves the results in the literature.

Key words: singular second order nonlinear differential equation, periodic boundary value problem, existence of positive solution