The present study explored the impact of flipped classroom on English as a foreign language (EFL) students' global writing performance and writing complexity, accuracy, and fluency (CAF) through a quasi-experimental research design. In so doing, two intact classes were selected from an Iranian university as the participants of the study and they were randomly assigned as the control and experimental groups with 24 and 27 EFL students respectively. Over a period of one semester, the control group (the non-flipped classroom) was taught using traditional writing instruction whereas the experimental group (the flipped classroom) was taught in a flipped learning mode. The students' performance on two timed writing tasks was examined in terms of global writing performance and writing CAF. Paired samples t-tests, one-way ANCOVA, Mann Whitney U, and Wilcoxon Signed Rank tests were used to analyse the data. The results demonstrated that the flipped classroom significantly developed and outperformed the non-flipped classroom on EFL students' global writing performance and writing fluency; however, its effect on the students' writing complexity and accuracy fell short of significance. Based on the findings, implications are provided for EFL writing instruction.