Students need more independent roles to evaluate their learning performance, especially in the absence of teachers' feedback due to some constraints such as technology and poor experience. This study investigates the potential of online self-evaluation on students' writing skills in English as a foreign language (EFL). It examines the preparatory year (PY) level one students' most improved EFL writing areas and perceptions when they use online self-evaluation in writing. In this quasi-experiment, two groups of PY EFL writing program students (N = 60) participated in the study for the first semester 2020-2021. A mixed-method design was applied: Self-monitoring checklists, self-evaluation questionnaires, achievement tests, and students' portfolios. Findings revealed that most of the learners' mistakes were in punctuation marks, capitalization, informal language, and subject-verb agreement. It was also perceived that learners were doing fine about where and how they should be. The study proved that the students' self-evaluation and performance in writing correlated significantly; however, the effect size was low. Based on the research findings, it is recommended that training programs on strategy are to be boosted, especially in institutions where learners receive less feedback.