The purpose of this study is to verify if there is any difference on researchers' language preference for citing documents in different subject fields. 8 scientific journals were selected one of each from 8 main categories, given by National Research Foundation of Korea. Five variables including the rate of citing domestic and foreign documents for each journals were choose, and the differences on language preference among researchers of different subject fields were checked by implementing ANOVA. As a result, there are some differences on language preference, in terms of the average number and percentage of foreign documents, among researchers, based on their subject background. It also found that 8 subject categories divided into 4 small clusters.