Puppies antibody titer response to Canine Distemper virus (CDV) before and after vaccination with a CDV-combined vaccine was studied using a serum neutralization test (SN). A total of 201 samples were obtained from puppies at the Small Animal Hospital, Faculty of Veterinary Science, Chulalongkorn University. The result showed that 100%(82/82) of the puppies, before vaccination, had no detectable SN titre (CDV SN-titer 0.05).