The Airbus A380 superjumbo, carrying 263 passengers, landed safely at Changi airport, an airline spokesman said. The passengers were transferred to another flight which took off at 5pm local time.
Flight SQ866 returned to Changi "as a result of a cockpit warning relating to a cargo door", the Singapore Airlines (SIA) spokesman said.
"SIA engineers are currently troubleshooting to find out the cause of why the warning came on."
SQ866 is a daily flight from Singapore that normally departs at 1pm local time.
Singapore Airlines has 19 A380s with five others on order, operating on routes from Singapore to various destinations including Hong Kong, Frankfurt, London and Los Angeles.
In January, one of the airline's A380 fleet was forced to make an emergency landing in Azerbaijan after suffering a drop in cabin pressure. SIA said an investigation was focusing on a main deck door that appeared to have suffered a leak.