Muc1 is the cell surface glycoprotein abundantly expressed in cancer cells and has been shown to be involved in tumor metastasis and promotion. Recently, we identified a 37 bp segment on the hamster Muc1 promoter with the ability to suppress Muc1 transcription. This 37 bp putative negative regulatory element (NRE) binds to a transcriptional regulator Yin Yang 1 (YY1). In the present study, we examined whether binding of YY1 is responsible for the negative regulatory effect by the 37 bp segment using a hamster pancreatic cancer cell line, HP-1 cells, transfected with various expression plasmid constructs. Our results showed that: (1) overexpression of YY1 up-regulated the transcriptional activity of the full-length hamster Muc1 promoter in a dose-dependent manner; (2) the mutation of the YY1 binding site did not affect either the basal transcriptional activity or the increased transcriptional activity by YY1; and (3) even the deletion of the 37 bp NRE segment could not abrogate the increased transcriptional activity by YY1. We conclude that the NRE acts in a YY1-independent manner and that YY1 instead enhances Muc1 transcriptional activity. Further study of the precise mechanism by which YY1 augments Muc1 gene expression should be worthwhile.