The aim of this study is to investigate the influence of grammatical gender on Russian speakers’ cognition, compared with Thai speakers’ cognition by means of object categorization. The key materials in the experiment are black-and-white pictures represented by nouns that are selected based on gender and appearance similarity. The hypothesis is that Russian speakers group two pictures that belong to the same grammatical gender class together, while Thai speakers generally rely on the size or shape of objects in the pictures. The result of the experiment statistically showed that Russian speakers categorized things on the basis of grammatical gender, while Thai speakers categorized things represented by things grouped on the basis of size or shape. Additionally, the result implies that bilingualism is a very important variable in a study testing the Linguistic Relativity Hypothesis.