Previous studies of both adult and child bilinguals have suggested that there is form similarity effect in the processing and acquisition of translation equivalent (TE) words. However, few studies are available on this effect in very young children acquiring a pair of linguistically distant languages. The present study aimed to examine such effect in very young children acquiring two distant languages, Japanese and English, with the hypotheses that if such effect plays a role in bilinguals’ vocabulary acquisition, acquisition of form similar words is facilitated more in comparison to form dissimilar words, and that young bilinguals may have more form similar words than non-form similar words in their vocabularies. Overall 12 children aged 24-36 months were organized into a bilingual group and a monolingual group. The data on children’s productive words in Japanese and English were collected using English and Japanese versions of CDIs answered by their parents. Comparing the words on both language versions of CDIs, the only overlapping words with similar or same meaning were treated as TEs and subcategorized as form similar (FS) or content similar (CS). The percentages of productive FS and CS were compared both between the language groups and also within each group. It was found that bilingual group had more FS, and the monolingual group had more CS. Also, the bilingual group had more FS than CS, whereas the opposite trend was apparent for the monolingual group, suggesting the form similarity effect. The present study is one of few studies demonstrating the form similarity effect in acquisition of vocabularies in bilingual children acquiring a pair of vastly distant languages. This implies the existence of cognitive process that supports bilingual language acquisition.