The surcharges are VND5,000 (20 U.S. cents) for each GrabBike trip and GrabFood order in some localities including HCMC, Hanoi, Hai Phong, Da Nang and Can Tho.
GrabExpress services in HCMC and Hanoi will attract a surcharge of VND3,000 for each delivery.
The surcharge will be applied "during extremely hot weather", Grab said on its website without disclosing further details.
The Singapore-based ride hailing firm is the first to roll out surcharges for hot weather conditions. Earlier, a surcharge of VND10,000-15,000 has been applied for late nights and the Lunar New Year holiday.
In early March this year, Grab had raised all fares by VND500-2,500 to aid drivers coping with surging gasoline prices.