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Circular RNAs (circRNAs) represent a class of non-coding RNAs that are widely expressed in mammals. However, it is largely unknown about the function of human circRNAs and the roles of circRNAs in human oral squamous cell carcinomas (OSCC). Here we performed a comprehensive study of circRNAs in human OSCC using circRNA and mRNA microarrays, and identified many circRNAs that are differentially expressed between OSCC tissue and paired non-cancerous matched tissue. We further found a circRNA termed circRNA_100290 that served as a critical regulator in OSCC development. We discovered that circRNA_100290 was upregulated and co-expressed with CDK6 in OSCC tissue. Knockdown of circRNA_100290 decreased expression of CDK6 and inhibited proliferation of OSCC cell lines in vitro and in vivo. Via luciferase reporter assays, circRNA_100290 was observed to directly bind to miR-29 family members. Further EGFP/RFP reporter assays showed that CDK6 was the direct target of miR-29b. Taken together, we conclude that circRNA_100290 may function as a competing endogenous RNA to regulate CDK6 expression through sponging up miR-29b family members. Taken together, it indicates that circRNAs may exert regulatory functions in OSCC and may be a potential target for OSCC therapy.