This study explores the degree of language knowledge of Japanese living in Catalonia and their perceptions of the two particular languages used in this multilingual/bilingual society. The data on language proficiency was obtained via a questionnaire survey which was evaluated by the subjects themselves and analysed by means of correspondence analysis. A significant correlation between the degree of knowledge of Castilian and that of Catalan was found, suggesting 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 learnt by a particular group of subjects who had achieved a certain level in Castilian. Furthermore, in-depth interviews were conducted to determine how the subjects perceive Catalan and Castilian. Commonly, they were perceived in a dichotomous way, with Castilian being a wider-used language and Catalan being a language of limited use not meant for outsiders. Castilian is learnt rather unconditionally, probably because it is the Spanish state's language, which mirrors the traditional language ideology of Japan--one nation, one language. The majority of the subjects had not learnt Catalan for various reasons such as priority given to Castilian and behaviour of the local population.