This study aims at assessing the English vocabulary size and strength of primary pre-service teachers using Computer Adaptive Test of Size and Strength (Laufer: 2004). The group for this study is 46 freshmen of a National University of Education. The results of the study are as follows. First, the average vocabulary size of the group is 10646 and the gap between the highest size (13350) and the lowest size (7750) is 5600. This wide spread of the vocabulary size of the students shows that the level of the students’ vocabulary knowledge is quite various. About 50% of the students is included in the range of 10000-11999. Second, the average vocabulary size of the group in the productive recall dimension is 6430 and the gap between the highest size and the lowest size is 11000, compared to the 5600 gap in the overall test. This wider gap in the productive recall dimension indicates that the levles in this dimension is the biggest among the four dimensions. Third, S30, whose vocabulary size is the closest to the average, has the vocabulary size of 10650; 5400 in the productive recall, 3300 in the receptive recall, 1850 in the productive recognition, and 100 in the receptive recognition. As the level increases in the frequency, the vocabulary strength of the productive recall dimension decreases.