This　paper　studies　event-based　attitude　regulation　design　for　uncertain　rigid　spacecraft　in　terms　of　Rodriguez　parameters.　First,　an　input-to-state　stabilizing　controller　is　developed　to　quantify　the　effect　of　sampling　error,　allowing　us　to　embed　an　event-triggering　mechanism　by　virtue　of　this　specific　external　stability.　It　leads　to　a　valid　event-triggered　controller　for　attitude　regulation　with　any　specified　precision.　A　numerical　example　is　presented　to　illustrate　the　effectiveness　of　the　proposed　algorithm.　©　2019　JSME.