This study aimed at investigating the role of Mobile-based Email in improving Ajloun College English Students' Achievement. It attempts to answer the following questions: What is the potential contribution of mobile-based email exchanged to writing skills? What is the potential contribution of mobile-based email exchanged to vocabulary acquisition? To answer these questions, the researchers carried out a project based on Mobile-based Email for the experimental groups. Thirty students were purposefully chosen from two universities (Al-Balqa Applied University and Jerash University) in the first semester of the academic year 2011. The instrument of the study was a survey. To establish the validity for the instrument, the method of content validity was used by giving it to a jury of specialists. Means scores and standard deviations of the participants' responses on writing and vocabulary were used to examine the significance of the treatment on the dependent variables. The results revealed that the writing skills and vocabulary of the students in the experimental groups significantly improved. On the basis of the results of the present study, the researchers propose a number of recommendations and makes suggestions for future research. (Contains 3 tables.)