We have previously shown that some commonly consumed substances, present in the average human diet, might cross over the placental barrier and affect the development of embryo immune system. The aim of the present study was to examine the cellular and humoral immune response in the group of offsprings from mothers treated with caffeic acid (1 or 6 mg/day) during pregnancy and lactation. We observed that the mean spleen relative weight was reduced in 4-week old progeny of mice treated with 6 mg/day of caffeic acid. The percentage of spleen CD3⁺ lymphocytes was decreased in both examined doses, while the number of CD19⁺ lymphocytes was not affected. Local G-v-H reaction induced by splenocytes from 4-week old progeny of caffeic acid–treated mothers was significantly suppressed in both dosage groups. Caffeic acid feeding (6 mg) resulted in up-regulation of the peripheral blood granulocytes chemiluminescent activity as well as in the enhancement of anti-SRBC antibody production in the 6-week old progeny of the treated mothers. We concluded that caffeic acid-enriched mothers’ diet may affect progeny immune system function in the postnatal period.