In the literature on L2 collocational processing, the influence of L1 activation has been subject to considerable discussion. Using an acceptability judgment task, this study assesses the effect of L1 activation in three different types of collocations: (a) English-only collocations that cannot be directly translated into Japanese (e.g., flat rate-??平らな割合), (b) congruent collocations (e.g., cold tea-冷たいお茶), (c) Japanized collocations (e.g., ??yellow voice-黄色い声援). The results indicated that L1 activation was evident regardless of both the proficiency level and the collocation types. The learners were more likely to accept collocations that they thought were easily translated into Japanese even for English-only collocations. Moreover, even highly-proficient Japanese learners of English did not properly reject the Japanized collocations, suggesting that those items are difficult to acquire without negative evidence that is not available in natural input.