The study aimed at comparing the effect of oral somatostatin 14 (SS-14) and somatostatin 28 (SS-28)DNA vaccines in promoting lactation of rats. Fifteen female SD rats were randomly divided into three groups and were orally vaccinated, respectively SS-14 (Group T1) and SS-28 (Group T2) DNA vaccines fused tPA signal peptide and CpG adjuvant and delivered by attenuated Salmonella choleraesuis at weeks 0, 3 and 6 of the study, and rats in control group (Group C) was orally given empty vector vaccine. Blood samples were collected before primary immunization and at weeks 3, 5 and 7 after primary immunization and body weight of offspring were weighed at weeks 0, 2 and 4 after birth. Both SS-14 and SS-28 DNA vaccines induced humoral immune response, however, antibody response in T1 group were significantly stronger than that in T2 and C groups. Serum GH levels in T1 group was significantly higher than those in T2 and C groups, and serum PRL levels in T1 group was significantly higher than that in control group. Body weight of offsping rats in T1 group were significantly higher than that in control group at weeks 2 and 4 after birth, and body weight of offsping in T2 group were significantly higher than that in control group only at week 4. Oral SS-14 DNA vaccine fused tPA signal peptide and CpG adjuvant and delivered by attenuated Salmonella choleraesuis was more effective than that oral SS-28 DNA vaccine in promoting lactation of rats.