This paper is a cross-disciplinary study of evidentiality in English abstracts. The corpus consists of 200 abstracts of English RAs of four disciplines: linguistics, philosophy, computer and electronics. Firstly, our study presents the lexicogrammatical realizations of evidentiality in English abstracts of four disciplines, and then it compares the cross-disciplinary use of evidentiality from the analyses of reporting evidentials and modal verbs in inferring evidentials. The analyses show significant differences in the distribution and frequency of four evidential types in abstracts of the four disciplines and also show that different disciplinary conventions of writers may influence their choice of evidentiality in their abstracts writing. It is hoped that this study may be helpful to enrich the study of evidentiality in academic discourses. Besides, it may give implications on the learning and teaching of academic writing.