In an attempt to measure the dynamic features of foreign language enjoyment (FLE), we adopted a longitudinal confirmatory factor analysis-curve of factors model (LCFA-CFM) approach to substantiate the validity of the original FLE scale (Dewaele and MacIntyre [(2014. "The Two Faces of Janus? Anxiety and Enjoyment in the Foreign Language Classroom." "Studies in Second Language Learning and Teaching" 4 (2): 237-274]) longitudinally and trace changes in this construct at different points of time in an English as a foreign language (EFL) course. This approach ensures measurement invariance over time and deals with second order latent variables. The data were collected from 437 adult EFL learners in four time phases using FLES and were analyzed by Mplus with LCFA-CFM. The model fit was accepted and the invariance of the latent factor was confirmed over time. The negative covariance between slope and intercept (second order latent variables) suggested that learners with lower initial FLE experienced a faster increase in FLE over time, as the mean of slope was larger than that of the intercept, which can be influenced by learner's motivation, changing attitude to L2 learning and the supportive role of the teacher. The key strength of this research lies in the longitudinal confirmatory factor analysis performed to capture the temporal growth of FLE and how it evolved through the L2 course.