The study aimed to investigate if there was a motivational difference between Turkish students and international students for learning English at a prep-school of a state university in Turkey in terms of attitude, integrative orientation, instrumental orientation, altruistic motivation and parental encouragement. It was also carried out to find out if there was a relationship between the students' motivational level and their performance in English. 20 Turkish students and 16 international students participated in this study. The data was collected through an adapted questionnaire and the students' midterm exam results were obtained as a sign of their performance in English. The analysis of the quantitative data revealed that although both groups had high mean scores on the questionnaire, the mean of the Turkish students' motivational level for learning English was lower than the mean of the international students'. It was also found that while there was a statistically significant difference regarding integrative orientation and altruistic motivation between the groups, there was no statistically significant difference regarding attitudes towards learning English, instrumental orientation and parental encouragement. In addition, the Pearson Correlation did not disclose a significant correlation between the groups' scores in the mid-term exam and their mean scores on the questionnaire. Another purpose of the study was to discover what motivated and demotivated both groups most in English courses. Minute papers were conducted for this purpose and the findings showed many motivating and demotivating factors. Based on the results, some implications were presented and discussed.