This paper explores the question of how cultural stereotypes are formed, modified, dismissed or reinforced, drawing on findings from a collaborative intercultural e-mail project between Hong Kong learners of Japanese at The Hong Kong Polytechnic University and native Japanese speakers at Kagoshima University. It also evaluates role of e-mail assisted projects in breaking down the stereotypes. Analysis of the data collected from e-mail exchanges, project reports and interviews with the participants suggests that, first, the cultural assumptions of learners are formed on the basis of various types of inputs from the target culture. Second, the level of assurance that the learners felt about the accuracy of cultural representations appears to be related to the types and origins of the input from the target culture. Third, there may be a hierarchical relationship of inputs in terms of the degree of impact each type of input from the target culture has on forming the cultural stereotypes of learners. Those based on remarks from native speakers and classroom teaching appear to be more influential than those based on the mass media and hearsay from fellow learners. Fourth, although the project enabled the learners to validate and modify their previous assumptions, it also created new stereotypes or reinforced existing ones.