For approval of generic drugs, the U.S. Food and Drug Administration (FDA) requires the evidence of bioequivalence in average bioavailability from the bioavailability/bioequivalence studies. The criterion for assessment of bioequivalence adopted by the FDA is a moment-based criterion evaluating log-transformed pharmacokinetic responses such as area under the blood or plasma concentration-time curve (AUC) or maximum concentration (Cmax). Unlike traditional small molecule drug products, the characteristics and development of biologic products are more complicated and sensitive to many factors. Thus, it is of concern to know whether the current bioequivalence criterion is applicable to the assessment of biosimilarity between biologic products. In this article, we compare the moment-based criterion with a probability-based criterion proposed by Tse et al. (2006) for assessment of bioequivalence or biosimilarity between two drug products in terms of consistency/inconsistency for correctly concluding bioequivalence or biosimilarity. A simulation study was conducted to study relative performance of the two criteria. The feasibility and applicability of the proposed criteria for assessment of biosimilarity of follow-on biologics are discussed.