This study is aimed at investigating the level of teacher-written feedback self-efficacy among Malaysian secondary school teachers and the influence of teachers' age, gender, qualifications and teaching experiences on their written feedback self-efficacy. Bandura (1986) had mentioned that of all the different aspects of self-knowledge, none is more influential in people's everyday lives than their personal self-efficacy. People with a high level of self-efficacy expect favourable outcomes, while those who doubt themselves expect mediocre performance, which results in negative outcomes. This research examined the impact of self-efficacy on teacher-written feedback in formative assessment. Self-efficacy is very important to determine how teacher-written feedback is placed in their formative assessment. One hundred sixty-six English language teachers in Selangor participated in this research by completing the survey. This current research reveals that secondary schools' English teachers' self-efficacy of teacher-written feedback was mostly unrelated to their demographic factors. The results have shown that there was no significant difference among Malaysian secondary school teachers in relation to their qualification, teaching experience and level of training in written feedback self-efficacy.