Investigations into the development of critical thinking (CT) skills in L2 writing have attracted much attention in the field, with more recent studies supporting the view that the quality of CT is modulated by L2 proficiency, not by the structure nor cultural properties of the learners’ L1 (Manalo & Sheppard 2016).  However, the properties of CT skills among early bilinguals have received little attention despite its increasing importance in educational settings.   The current study examines the quality of persuasive writing as a manifestation of CT in Japanese-English early bilingual college students who have developed literacy skills in both languages. Students are asked to write persuasive essays in each language on separate days on the pros and cons of a controversial issue. The essays are evaluated in terms of persuasiveness (Miller et al 2019) and the quality of CT (Paul & Elder 2013), and are analyzed if there are differences between the essays in different languages, and if language dominance impacts the quality of persuasion and CT.  Our analyses reveal that the participants exhibited higher level of persuasion in the dominant language, but CT quality is mostly similar between the two languages.  The results support the view that a better control of the language leads to better performance in persuasion, but the quality of CT is not affected by language proficiency. The current findings suggest that the influence of language dominance on CT skills tends to be limited in early bilinguals.