Communication relays have been used for the control of low level circuits, and organic gases vaporized from relays or contamination of contact surface were studied as the factors lowering contact reliability so far. Conversely, contact materials of platinum group contacts like palladium and gold or silver alloy contacts were mainly evaluated as reliable contacts. Authors tried to clarify the contact failure mechanism of gold or silver alloy contacts at a extremely low electrical load which had minimal switching electrical energy. As a result, the oxides are detected from contact failure samples by the contact surface analysis, which suggests a small amount of impure substances in the gold alloy causes contact resistance increase. In addition, the influence of the ratio of oxygen and nitrogen on contact resistance was investigated. Then the contact failure has not occurred below 0.1% of oxygen concentration. As for some contact materials, the permissible contact force was also studied.