In this paper we investigate further properties of the de-FORMABLE derivative and use the results to study the existence of solu-tions to the integro-di , erential equation D , R y(t) = h(y(t))+f(t,y(t))+ t 0 K(t,s,y(s))ds,t 2 [0,T], with initial condition y(0) = y0,where D , y(t) is the deFORMABLE derivative of y, 0 < ,< 1. We useWeissinger's , xed point theorem and Krasnoselskii's , xed point theorem to achieve our main results. An example is provided for illustration.