Abstract: Tribological behaviors of 45~# steel-steel pair under presence of Mg_6Si_4O_(10)(OH)_8 as an additive dispersed in API SD/CC/SAE40 engine oil were investigated. Tribological experiments were carried out on a Falex friction and wear tester in ring-on-ring contact configuration for about 400 h including 11 experimental stages. Wear and micro-hardness of the worn surface were measured after every experimental stage; cross section of the worn surface was observed and analyzed with SEM and EDX after the whole tribological test. According to the variations in friction coefficient, wear rate, temperature of tribo-pair and tribo-surface micro hardness with time, the tribological process lubricated by oil containing Mg_6Si_4O_(10)(OH)_8 shows quasi-periodicity with characteristic of damped oscillation, and quasi-period is 200 h; micro-hardness of the worn surface is one time higher than that of 45~# steel substrate. SEM and EDX results showed that a 3~6 m thickness recovered layer with high C and O content could be generated on the 45~# steel tribo-surface.