Abstract: A new sufficient conditions are derived for the existence of positive periodic solution ofneutral delay model of the formN′(t)=N(t)[ (t)- (t)N(t)-b(t)N(t- (t))-c(t)N′(t- (t))]where (t), (t), b(t), c(t), (t) are nonnegative continuous T-periodic functions, and the result in this paper answerthe open problem 9.2 in [1].