Integration of technology which includes the use of a smartphone is currently one of the trends in ESL writing classes. Particularly in collaborative activities, it is assumed that the use of smartphones contributes to the attitude of the learners towards writing and their writing performance as well. Consequently, the present study investigated the writing performance of ten gender-mixed groups who used smartphones as they engaged themselves in a collaborative essay writing activity. Likewise, through a focused group discussion, attitude of the learners towards writing was determined. Results revealed that the collaborative essay writing activity which used smartphones had a positive influence on the content, organization and vocabulary of the essay. However, no influence was seen in grammar and mechanics. Learners reported a positive attitude in writing in terms of affective, behavioral and cognitive aspects.