We report a long-term lubrication for a PbS QD nanocoating sliding against bearing steel balls in the air. Through tribo-physchemical interactions, ultralow friction (μ ≈ 0.078 ± 0.0026) is achieved for the system tested under 1 N for 60 min. During the rubbing process, the tribo-film of the counterfacing ball is covered by a degraded PbS QD layer and amorphous mixed phase. Meanwhile, the disc track surface is composed of degraded PbS QD layers, clustered rearranged PbS QD districts, induced decomposed Pb-enriched multilayers, and an amorphous mixed phase via friction-induced structural transformation. The PbS QDs are transferred onto the sliding contacts to form a robust tribo-film, which is the key to realizing ultralow friction. Consequently, a long-term lubrication mechanism is attributed to the synergetic tribo-physchemical interaction along sliding interfaces upon shift, redirection, and decomposition of nanoparticles. These discoveries reveal QD-based nanolubricants in common working conditions for mechanical engineering.