The existence of positive solutions are obtained for boundary value problems of impulsive differential equation
-y″(t)=f(t,y(t)), t∈[0,1]\{t1,t2,…,tm},
Δy′(tk)=Jk(y(tk)), k=1,…,m,
y(0)=y(1)=0
where f can change the sign. The proof is based on the fixed point index theorem in cones. The results of this paper improve and generalize the known results in the literature.