We report dewetting behavior of thermally annealed thin polymer strips of poly (styrene-b-butadiene-b-styrene) and polystyrene films that are laterally confined by polydimethylsiloxane walls on silicon substrate. Regularly spaced holes are initially nucleated on the polymer surface and then grow with the aid of the confining walls, resulting in the formation of distinctly observable, regularly spaced blocks of the strip. It is observed that the dependence of hole density on the film thickness severely deviates from the conventional capillary wave model. This anomaly may be related to the viscoleastic properties of the polymer film.