A lubricating oil for two-cycle engines, which comprises a polyoxyalkylene glycol derivative represented by the following formula as a base oil, can be used to lubricate bearing portions and frictional portions of an two-cycle engine, so that the engine can be remarkably improved in generation of smoke, starting performance, cleanliness to prevent its exhaust system from clogging with carbon, cleanliness at high- or low temperature, and anti-seizure performance. ##STR1##