Electronic devices have been used under various thermal conditions in space applications. The temperature range often exceeds 100 "C, and the electronic devices are stressed by both high and low temperatures and thermal cycles. Since repairing and reworking of the spacecraft electronic hardware cannot be performed after launch, verifying the reliability of the hardware on the ground before the launch is essential. The thermal stresses to the electronic devices' solderedjoints have recently tended to increase because the devices must be made smaller and lighter. The thermal fatigue of the soldered joints must be addressed in order to achieve highly reliable flight hardware. We studied a test method to estimate the thermal fatigue life of soldered joints for space use. This paper examines the thermal fatigue life using two kinds of test methods as heat-resistant evaluation tests of soldered joints for space use, and evaluates the effectof the test parameters on the thermal fatigue life of soldered joints. We conclude that the thermal fatigue life of soldered joints cannot be estimated accurately, if the test parameters are instituted uniformly.