A 23-year-old man has been jailed 21 months for stealing his mother's passport and selling it, together with his own.

Alan Chin pleaded guilty at the District Court to one count of theft and two counts of transferring Hong Kong Special Administrative Region passports to others without reasonable excuse.

The Immigration Department launched an investigation into Chin after a Mainlander, who posed as the defendant's mother and carried her passport, was deported from Turkey in April.

Chin admitted he sold the passports to an agent who advertised in a newspaper. He received $800 for each.