This research dealt with the effect of Sustained Silent Reading on improving the students’ vocabulary, reading, and grammar achievements. The participants of the study were the students studying at two Secondary Schools in Turkey in Kahramanmaraş province. In the study, it was investigated whether Sustained Silent Reading Strategies helped the EFL Secondary School learners to develop their reading comprehension, vocabulary, and grammar knowledge in Andırın/Kahramanmaraş. In this regard, the researcher provided the students with a variety of reading materials consistent with their language proficiency level and interests so that they could read silently. At the end of this study, the researcher measured the participating students’ reading, vocabulary, and grammar achievements on Sustained Silent Reading strategies and skills. The study consisted of two groups; an experimental and a control group. Both experimental and control groups consisted of 70 students studying at Torun Kastal and Şehit Yasin Höbek Secondary Schools. Totally the groups consisted of 140 students. The reading materials were handed out by the researcher and the experimental group students’ number of pages that they read during the SSR sessions was recorded. The experimental group of students totally read 20 elementary-level books of their own choice. The control group kept on their regular online English classes because of Covid-19. The results revealed that students in the experimental group improved their achievement levels in reading comprehension, vocabulary, and grammar knowledge. Moreover, the researcher applied different comprehension texts and multiple choice questions during two lessons of the time. The findings of the present study revealed that SSR could be a beneficial activity for ELT students to improve their reading comprehension, vocabulary, and grammar knowledge.