The main purpose of the current study was to develop EFL writing performance and critical thinking of the first-year secondary stage students by using a reflective writing protocol. The present study followed the quasi experimental research design (pre/posttest and experimental and control group). To achieve this end the researcher selected 50 EFL first year experimental secondary stage students randomly from Omar El-Farouk secondary school, Zagazig directorate, Sharkia governorate, Egypt. They were equally divided into two groups, 25 students for the experimental group and 25 for the control one. An EFL writing performance test was administered to measure EFL writing performance before and after the treatment, similarly, a critical thinking scale was administered before and after the treatment adopting the reflective writing protocol. This study lasted for the period of ten weeks during the second term of the school year 2021/2022. The findings of the study showed that the reflective writing protocol was effective in developing the EFL writing performance of the secondary stage students and increasing their critical thinking.