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This study aims to elucidate the synergy effects of the σ phase and carbide on the wear behavior of low-carbon (LC) and high-carbon (HC) cobalt–chromium–molybdenum (CoCrMo) alloys, by using pin-on-disc tests under Hanks' lubricated conditions. Fractured or torn-off σ-phase precipitates were observed to be the main reason for abrasion for both LC and HC alloys. Carbides were torn off at the initial high contact pressure to form pitting; σ-phase precipitates around the pitting were uprooted and led to micro cracks, which is considered as surface fatigue of HC alloy. In contrast, strain-induced martensite observed on the worn surface was contributed to the increase of hardness and abrasion resistance of LC alloy.