It bought 3.56 million shares from the State Capital Investment Corporation (SCIC) at VND97,500 per share in a deal worth almost VND350 billion.
SCIC had planned to auction the shares in July 2020 at a starting price of VND111,700 ($4.80), but failed to attract investor interest.
Sa Giang makes ready-to-eat foods such as prawn crackers and instant noodles and newer products such as crackers made from crab, fish and squid.
It mainly exports its products to Europe, especially Germany and the Netherlands, and some Asian countries.
Last year it reported revenues of VND310 billion and a net profit of VND31 billion.
The company has convened as extraordinary general meeting at the beginning of February to dismiss some members of the board of directors and the supervisory board and elect new ones.