Ignition phenomena of overloaded electric wires have been investigated in microgravity as basic information for fire safety in space. Microgravity experiments were conducted at MGLAB (Micro Gravity Laboratory of Japan) to provide 4.5s of microgravity time. In the experiments the current supply duration was selected as the main test parameter to simulate the status of the circuit breaker shortly after the overload occurs. Other important test parameters were the surrounding oxygen concentration and the supplied electric current amount. The results showed that the microgravity environment significantly increases the ignition probability, including the occurrence of delayed ignition and extended ignition limits, with large electric currents when compared with the situation under normal earth based gravity. The increase in the ignition probability is explained by decreases in the minimum ignition energy in microgravity interacting with the ignition mechanism.