The present research aimed to test an Amharic version of the multi-dimensional Work Task Motivation Scale for Teachers (WTMST), which measures the five pillars of university instructors' motivation toward teaching and student evaluation tasks based on self-determination theory (SDT). Therefore, the WTMST offers the first instrument to measure all five motivational elements, and today it is one of the most applicable instruments to assess teachers' motivation. An Amharic version of the WTMST for teaching and student evaluation tasks was adopted and assessed in large-scale data (N=1,117). Our findings demonstrate excellent reliability and construct validity (convergent, discriminant, divergent and factorial). Besides, the results of the model comparisons provided that out of the four theoretically competing models (single-order factor, correlated factor, higher-order factor and bi-factor models), the bifactor model was the most-fitted one used for measurement invariance across various groups. Results also suggest that the factor structure of the WTMST for both teaching and student evaluation tasks demonstrate consistency across gender (men, women), university types (research, applied, and general university), age and experience in teaching. Therefore, the WTMST for teaching and student evaluation tasks may be valid in Ethiopian higher education settings.