Star clusters provide astronomers with a unique opportunity to study the formation, evolution, and dynamic structure of a coeval ensemble of stars with more or less similar original chemical composition. These stars have the same age and move together with common trends.

Membership determination based on the proper motion data of observed stars can be obtained by apllying some methods given in the literature: Vasilevskis and Rach (1957), Sanders (1971), Zhao and He (1990) and Uribe and Brieva (1994).

Relative proper motions of stars within an area of 14' of diameter centered in the cluster are determined by combining positions of stars observed at the Valinhos CCD meridian circle with positions given by other astrometric catalogues.

Our basic material to first epoch of stars brighter than V = 13 mag is the AC2000 Catalogue, which provides a time lag of about 90 years, whereas the USNO-A2.0 Catalogue is used for fainter stars, providing a time lag of about 40 years for the north hemisphere and 20 years for the south hemisphere.

Average accuracies in individual star' s proper motion of 2 mas /yr and 7 mas/yr are achieved, respectively, when the AC2000 or the USNO-A2.0 is used.

In this study we analysed the young open clusters NGC 1662, NGC 6834, NGC 6994 and IC 2581.