For one who holds a Chinese passport and US green card, is a visa required to visit Macau for a few days?

Answer 1

Since 1999, Macau is part of your country, despite its unusual status (like Hong Kong).
Stop trolling . . .

Answer 2

you should contact the immigration/customs office, not the airheads on Y!A.... to the best of my knowledge, a visa is only required for visits that are 4 weeks or more? not sure though.... but!! know who would know every detail you need? a immigration/import-export/Customs agent at the place youre going.