The monk, from the Drukpa Kagyu school of Tibetan Buddhism, which is different from that followed by Tibetan spiritual leader the Dalai Lama, was travelling from Kolkata via Singapore to Hong Kong, where he planned to apply for a Taiwan visa.
During his detention, the monk was only allowed to make a two- minute telephone call to his cousin, Hong Kong resident Phurba Sherpa, before being put on an aircraft and returned to Singapore.
Sherpa said that his cousin had visited Hong Kong several times and went last year to China for 20 days without any problem.
An Immigration Department spokesman said that the department would not comment on individual cases. He said it acted within the law and would only refuse entry "if necessary" and after taking all factors into account.