The aim of a study was to determine the efficacy of the microbial feed additive containing spores of Bacillus licheniformis and Bacillus subtilis (BioPlus 2B ® ) on performance and health status of rearing calves. Sixty four female Holstein calves, aged on average 16.7 ± 4.5 days, were randomly assigned into two groups of 32 animals: control (C) and BioPlus 2B ® (BP). Milk replacer (MR) and starter mixture (SM) fed to BP group contained 1.32 × 10 9 (±3.2%) and 1.13 × 10 9 (±11.5%) spores of Bacilli strains, respectively. Each calf was fed with 2.25 l of MR two times a day for eight weeks, up to the age of approximately 10 weeks. Starter diet (SD) offered to calves consisted of SM and whole maize grain, which were mixed in ratio 50:50 (wt/wt). Intake of MR was equal in both groups, but SD intake was higher in the whole experiment in the BP group (1075 vs 951 g/d; P<0.01). The BP calves grew faster than C ones in the whole trial (P=0.05), but especially in weeks 3-4 (P<0.05). At the end of the trial the BP calves were about 2.9 kg heavier than the C ones (P<0.001). Feed efficiency, calculated as consumption of ME (MJ) or crude protein (g), was not different between treatments. There were also no differences in the health status and faecal score between treatments. The results of this study suggest the beneficial effect of microbial feed additive containing spores of Bacillus licheniformis and Bacillus subtilis for rearing calves. PROBIOTIC FEED ADDITIVE -CALF PERFORMANCE