Before beginning human clinical drug trials, researchers need to conduct extensive preclinical studies involving animal experiments to preliminarily clarify each drug’s effects, toxicity, and pharmacokinetics. In addition to general considerations related to study design, the calculations for determining the appropriate sample sizes are a core element of experimental studies. Currently, there is a great deal of randomness in the selection of animal sample sizes, which not only leads to a reduction in the reproducibility and representativeness of experimental result but also causes funds to be wasted. Therefore, in this paper, we divide medical experimental research into exploratory and confirmatory studies and provide examples of sample size determination method based on the literature and our experience. Precision analysis, two-sample mean, resource equation, and KISS approach determination method are described with the aim of providing a calculation scheme for the selection of sample sizes and, therefore, reduce unnecessary harm to animals and improving the accuracy of the experiments. With the development and dissemination of combinations of medical statistics and medical experiments, research on the determination of animal experimental sample sizes will become increasingly perfected, providing firm theoretical and experimental bases for a rigorous research process and reliable conclusion.