The present research aimed to explore the dynamic growth of two emotional constructs: foreign language enjoyment (FLE) and foreign language learning boredom (FLLB) among L2 learners. To do so, we used a method that would capture the inherent dynamicity of L2 learners' enjoyment and boredom during an EFL course. To this aim, a bivariate latent growth curve model (LGCM) was employed to examine the covariance between 412 EFL learners' initial and growth levels of FLE and FLLB on four measurement occasions at two-week intervals. To collect the data, the original FLE scale and the newly developed FLLB scale were used. The model including the covariance between intercepts and slopes of FLE and FLLB was tested in Mplus 7. The analysis of the data revealed that the covariance between the intercept and slope of the FLE and FLLB was statistically significant and negative. This attests to the existence of a parallel process (co-variance) of FLE and FLLB, which indicates that an increase in the level of FLE among the participating L2 learners was strongly associated with a decrease in the level of FLLB during the whole course. The findings and implications are discussed in light of the existing literature.