The study aimed at assessing teaching stress on in-service teachers' motivation and its implication for quality education in Ethiopian Secondary Schools. A correlational research design was employed. The target population for this study was one higher learning institution's three college in-service teachers who attend their upgrading degree. 358 in-service teachers were sampled out of 1078 by stratified random sampling technique to collect pertinent information through a questionnaire. Firstly, about 69% of the in-service teachers were frustrated by teaching stress; secondly, about 70% of them failed to feel responsible for low results scored by students; thirdly, about 79% of them were poorly motivated in the teaching profession. Finally, it was found that there was statistically a significant strong negative relationship between teachers' level of motivation and causes of stress (workload, resources constraints, time pressure, students misbehavior and large class size), [rho] (354) = -0.75**, [rho] (354) = 0.73**, [rho] (354) = -0.72*, [rho] (354) = 0.72** and [rho] (354) = -0.80**, [rho] < 0.05. Therefore, to sustain the quality education in Ethiopia, all education stakeholders should search for mechanisms to minimize teaching stress and increase teachers' motivation through providing professional training, incentives, and privileges in type and in kind.