L2 writing scholars have recently debated the appropriateness of using cultural constructs to enhance the teaching of English. An important aspect of writing, critical thinking, has received considerable attention. Some have suggested that Asians, including Japanese, do not display critical thought in their writing in English. Other researchers claim that Asians display critical thinking abilities differently than Western learners. In addition, they argue that learners from a particular culture are too diverse to make claims about the whole group's thinking abilities. This study proposes a model for assessing critical thinking in the writing of L2 learners to determine whether content familiarity plays a role in critical thinking. Findings of a study of 45 Japanese undergraduate students indicate that the quality of critical thought depended on the topic content, with a familiar topic generating better critical thinking. Results also suggested that differing assumptions between the L1 and L2 culture may lead to misinterpretations of the critical thinking ability of L2 learners.