Objective: To determine the levels of workload and fatigue and the relationship between these two complex constructs among Constant Velocity (CV) joints assembly operators in Mexico. Methods: A cross-sectional and descriptive study was conducted. National Agency and Space Administration-Task Load Index (NASA-TLX) and Swedish Occupational Fatigue Inventory-Spanish (SOFI-S) version methods were applied to assess workload and fatigue, respectively. Non-parametric statistical tests were used to data comparison and correlation analysis. Results: A total of 116 workers were recruited. NASA-TLX and SOFI-S instruments obtained high levels of internal consistency and sample adequacy. Mental Demands, Overal Effort and Physical Demands obtained the highest workload scores while Performance obtained the lowest workload score. The Overall Workload Level (OWL) showed that 47% of the workers perceived the workload as high and 52% as very high. Lack of Energy and Physical Discomfort fatigue dimensions obtained the highest scores, while Lack of Motivation fatigue dimension obtained the lowest score. Positive significant correlations were obtained between Physical Demands and Lack of Energy, Temporal Demands and Physical Discomfort, and Frustration with the six workload items. Conclusion: Although assembly of CV joints is considered as physical task, no significant differences between Mental and Physical Demands were found. A structure equation model and a cognitive task analysis are suggested to explore the causal relationships and the components of Mental Demands.