Multiple access interference (MAI) is a primary concern in optical coded division multiple access (OCDMA). To alleviate this issue, first cancellation stage of an optical serial interference cancellation (O-SIC) can be employed. In this paper, we investigate the effect of optical serial interference cancellation for the first cancellation stage on bit error rate (BER). We compare the first cancellation stage with the conventional correlation method by utilizing different threshold values with the various length and different number of users. We have successfully shown that the optical serial interference cancellation yields a better performance than the conventional correlation method by choosing the optimum value in the first cancellation stage. We provide the results of computer simulations showing the BER improvement when the first cancellation stage of optical serial interference cancellation (OP- SIC) is used over the cancellation technique. The comparisons are done for several numbers of users.