Yes!
Vietnamese, or Vietnam passport holders, require a visa to enter Mozambique. The safest option is to apply for a preliminary visa on www.evisa.gov.mz at least 2 weeks before travelling to Mozambique. In this application you will need to upload copies of your documents, bank statements, and accommodation reservations. If accepted you will receive an electronic preliminary visa that you can present when arriving in Mozambique.
The cost of the visa 9.837,00 MZN (about $155USD) and this amount is only payable on arrival. There are no application costs involved.
This is the cheapest option for a Vietnamese and is valid for 30 days. There are also options for 60 and 90 days.