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Inactivated bacterial vaccines may contain residual levels of formaldehyde, which may have adverse effects. Therefore, it is important to determine the residual level of formaldehyde to ensure product safety. A number of assays are available for the determination of residual free formaldehyde in inactivated vaccines, including acetyl acetone titration, ferric chloride titration, and the basic fuchsin test. In the current study, ferric chloride quantitative method was used to evaluate formaldehyde residue on 4 types of vaccine produced in the Bacterial Vaccine section in Veterinary Research Institute (VRI), Ipoh. Four types of vaccines tested were Hemorrhagic Septicemia oil (HS oil), Hemorrhagic Septicemia alum (HS alum) vaccine, Duck vaccine (DV), and Sheep and Goat Pasteurellosis vaccine (SGP). Results revealed formaldehyde residue in vaccines tested was between 1.289 g/L to 2.228 g/L (mean SD ±0.18). According to European Pharmacopeia, when formaldehyde has been used in the preparation, the concentration of free formaldehyde is not greater than 0.5 g/L. While the United States Code of Federal stated that it must not exceed 0.74 g/L unless a higher amount has been shown to be safe. In our study, all the vaccines has been tested for safety and potency test before being used on animals, and therefore, it is safe for vaccination purpose. Formaldehyde residue will be conducted for each batch of vaccines production to ensure its safety.