Objectives: To investigate whether serum fibroblast growth factor 21 (FGF21) levels can be used to predict the future development of major adverse cardiovascular events (MACEs). Methods: This study included 253 patients who received subsequent follow-up, and complete data were collected for 234 patients. Independent predictors of MACEs were identified by using the Cox proportional-hazards regression analysis. The prognostic value of FGF21 levels for MACEs was evaluated by Kaplan-Meier survival analysis. Results: Of 229 patients finally enrolled in the analysis, 27/60 without coronary artery disease (CAD) at baseline experienced a MACE, and 132/169 patients with CAD at baseline experienced a MACE. Among patients with CAD at baseline, serum FGF21 levels were significantly higher in patients with MACEs (p < 0.05) than in patients without MACEs. Kaplan-Meier survival analysis showed patients with a higher serum FGF21 had a significantly lower event-free survival (p = 0.001) than those with a lower level. Further Cox proportional-hazards regression analysis, including the traditional risk factors for cardiovascular disease, showed that serum FGF21 was an independent predictor of MACE occurrence. Conclusions: In patients with CAD at baseline, an elevated serum FGF21 level was associated with the development of a MACE in the future.