The genus Rhodiola (Crassulaceae) consists of many species, growing mainly in Asia and traditionally used as adaptogens and anti-inflammatory drugs. In order to elaborate herbal immunostimulator which could be safely given to pregnant women, we performed a study on immunotropic effects of feeding pregnant and lactating mice Rhodiola kirilowii extracts. This paper presents the results of the first part of our study – spleen content of selected polyphenols, spleen cellularity, splenocytes phenotype and their response to mitogens. Experiments were performed on adult inbred females of Balb/c strain, mated with adult males. Females, since copulatory plug was noted, up to the 28-th day after delivery were fed daily with 20 mg/kg b.m. water (RKW) or hydro- lcoholic (RKW-A) extracts of Rhodiola kirilowii. Results: 1. Significantly lower proportion of pregnant mice in experimental groups than in the control. 2. Cellularity of spleen and flavonol quercetin spleen concentration were significantly lower in experimental groups in comparison to the controls. 3. Flavanols ( (+)-catechin and epicatechin) levels were significantly higher in the spleens of experimental mice than in the controls. 4. Positive correlation between spleen cellularity and quercetin, and negative correlation between spleen cellularity and epicatechin content were observed. 5. Spleen mass and spleen lymphocytes phenotype and proliferation in RKW and RKW-A fed mice did not differ from the control. These results, together with suspicion of some embryo- oxicity, are worrying and eliminate the possibility of use Rhodiola kirilowii extracts for long-term treatment in pregnant females.