As more biologic products are going off patent protection, the development of follow-on biologics products has received much attention from both biotechnology industry and the regulatory agencies. Unlike small-molecule drug products, the development of biologic products is very different and variable via the manufacture process and environment. Thus, Chow et al. (2010) suggested that the assessment of biosimilarity between biologic products focus on variability rather than average biosimilarity. In addition, it is also suggested that a probability-based criterion, which is more sensitive to variability, should be employed. In this article, we propose a probability-based asymptotic statistical testing procedure to evaluate biosimilarity in variability of two biologic products. A numerical study is conducted to investigate the relationship between the probability-based criterion in variability and various study parameters. Simulation studies were also conducted to empirically investigate the performance of the proposed probability-based asymptotic statistical testing procedure in term of empirical sizes and powers. A numerical example is provided to illustrate the proposed methods.