The study aimed to investigate the effect of flipped classroom instruction on enhancing grammar and vocabulary learning of secondary commercial school graduates enrolled in a preparation course for obtaining a Commercial Diploma Equivalency Certificate (CDEC), Cairo University. The CDEC preparation course is designed in the light of EFL teaching goals specified by Ministry of Education for general secondary schools to prepare commercial school graduates for studying in higher education settings. The study used the quasi-experimental design. The sample of the study consisted of fifty-eight students assigned to two group; 29 controls, 29 experimental. Instruments included two equivalent grammar and vocabulary tests. The Implementation of the proposed program took a period of seven weeks. Despite drawbacks and challenges, results of the study revealed the positive impact of flipped classroom instruction on enhancing grammar and vocabulary learning for secondary commercial school graduates