In the animal kingdom, genetic similarity has been considered as a central factor to direct cooperative behavior. In toad tadpoles (Bufo japonicus), our behavioral analyses and genetic data showed that genetic similarities can explain aggregation preference with statistical significance. However, it is unclear how preference of individual level influences rule of collective behavior in vertebrates. In this poster presentation, to clarify the relationship between social preference and genetic similarity at the group level, we quantitatively analyzed the correlation between aggregation behavior and genetic similarity (mitochondrial DNA Cytochrome b region and Major histocompatibility complex class II alleles) in three different lineages of toad tadpoles. Furthermore, we introduce an assessment for the relationship in the behavioral traits of the tadpoles between two different situations, in the group and in the one-on-one. To analyze social interactions in the one-on-one, the mean distances and contact times of 192 tadpole pairs were measured. We examined whether tadpole pairs belonging to the groups which have performed strong aggregation preferences show a tendency to connect strong social interactions.