This paper presents a design of environmental stress screening(ESS) for a temperature compensated crystal oscillator(TCXO). From the field data analysis, it is estimated that early failures of TCXOs are due to the instability of frequency. A simulation study was made to identify the frequency characteristic of TCXO with defect in the manufacturing process, and thermal cycling is selected as an environmental stress for disclosing frequency shift. The design of experiment using orthogonal array is planned to find out the optimum screening parameters maximizing screening strength. Test samples with known frequency characteristics are prepared to measure the screening strength. Maximum and minimum temperatures are predetermined from the component specification, and temperature change rate, soak time, and the number of cycles are selected as control variables. The frequencies of samples are measured to verify whether defect-free TCXOs are weakened or destroyed. The optimum ESS maximizing screening strength is obtained, and the performances with and without screening are compared from the real manufacturing process through a follow-up study.