This paper examine the extent of language knowledge of Japanese living in Catalonia and their perceptions of the two specific languages, Castilian and Catalan, employed in this multilingual/bilingual society. The data on language ability was attained via a questionnaire survey which was assessed by the subjects themselves and assayed by means of correspondence analysis. A significant correlation between the extent of knowledge of Castilian and that of Catalan was found, proposing that Castilian is the first language that almost all subjects learnt upon their arrival in Catalonia or prior to arriving. Catalan, on the other hand, was only acquired by a specific group of subjects who had attained a certain level in Castilian. Furthermore, in-depth interviews were conducted to define how the subjects perceive Catalan and Castilian. Commonly, they were perceived in a dichotomous way, with Castilian being a broader-used language and Catalan being a language of rstricted use not meant for outsiders. Castilian is acquired rather unconditionally, presumably because it is the Spanish state's language, which reflects the traditional language ideology of Japan – one nation, one language. The majority of the subjects had not acquired Catalan for diverse reasons like precedence given to Castilian and conduct of the local population.