The effects of different preservatives on the keeping quality of antitetanic serum were investigated. The following preservatives were added; cresol 0.3%, cresol 0 4% phenol 0.5%. phenol 0.25%, phenol 0.5% and merthiolate 1:10,000, merthiolate 1:5000, sodium azide 1:10,000, sodium azide 1:8000, sodium azide 1:5000. Sterility test, to­tal protein, physical appearance, pH values, safety and potency test were studied on each product after one year of storage. In this study, it is proved that the best quality was seen in the antitetanic serum with cresol 0.4% and with sodium azide 1:5000. Both products were clear in appearance, completely sterile from aerobic, anaerobic bacteria, fungus and mycoplasma. They were potent and safe when injected in horses. While, antitetanic serum with phenol 0.5% although it was sterile, potent and safe for injection, it gave turbidity on storage.