The well-enclosed warehouse, used to store Farmhouse brand products, is situated on a one-rai block of land at Ban Nong Khong village in tambon Ton Pao of San Kamphaeng district.
Police said the attack was reported about 1am.
Footage from the company's surveillance cameras showed four men arrived in front of the warehouse on two motorcycles. One of them threw a grenade onto the parking area where 23 delivery vehicles were parked in a row. The grenade landed in a ditch, so the explosion caused little damage to the vehicles.
Another grenade was hurled into the middle of the parking area. Two vehicles were damaged by the explosion.
Pol Lt Col Thanandorn Withayawuthikul, a forensic police officer, said the grenades of of the RDG5 type made in Russia.
Police believed the attackers might be of same group that launched a grenade attack on a PTT petrol station in the heart of Chiang Mai and a Singha beer warehouse in Chiang Mai's Saraphi district in March this year.