Given a simple polygon P, its guard zone G (of width r) is a closed region consisting of straight line segments and circular arcs (of radius r) bounding the polygon P such that there exists no pair of points p (on the boundary of P) and q (on the boundary of G) having their Euclidean distance d(p,q) less than r. In this paper we have designed a time-optimal sequential algorithm to solve the guard zone problem. ©2007 IEEE.