The invention relates to a preservative for medical foods. The preservative is prepared from, by weight, 1-9 parts of staphylococcus aureus phage powder, 1-9 parts of escherichia coli phage powder, 1-9 parts of Salmonella phage powder, 1-9 parts of shigella phage powder, 1-9 parts of listeria phage powder, 1-9 parts of proteus bacteriophage powder, 1-9 parts of botulinum phage powder and 4-6 partsof an antioxidant. The preservative can specifically inhibit pathogenic bacteria of common contaminated foods, effectively prevent pollution of the medical foods, prevent oxidation of lipids in the medical foods, and be the antibacterial, anti-oxidation, safe and non-toxic side effect preservative for the medical foods.