Determining cell quantity is a common problem in cytology research and anti-tumor drug development. Asimple and low-cost method was developed to determine monolayer and adherent-growth cell quantities. Thecell nucleus is located in the cytoplasm, and is independent. Thus, the nucleus cannot make contact even if thecell density is heavy. This phenomenon is the foundation of accurate cell-nucleus recognition. The cell nucleus iseasily recognizable in images after fluorescent staining because it is independent. A one-to-one relationship existsbetween the nucleus and the cell; therefore, this method can be used to determine the quantity of proliferatingcells. Results indicated that the activity of the histone deacetylase inhibitor Z1 was effective after this methodwas used. The nude-mouse xenograft model also revealed the potent anti-tumor activity of Z1. This researchpresents a new anti-tumor-drug evaluation method.