The aim of the study was to search for antibiotic (erythromycin, tetracycline and/or kanamycin) resistance among lactic acid bacteria (LAB) and bifidobacteria isolated from children's intestinal mucosa. We were searching for signs of phenotypic or genotypic antibiotic resistance. First we homogenized intestinal biopsy samples and isolated LAB, bifidoacteria strains had already been isolated. LAB isolates were screened with RAPD to see how related they are, for further analysis we chose the ones with uniqe M13 bands. After DNA isolation and 16S rDNA amplification isolates were sent for sequencing to determine their genus or species. Further on, we tested the LAB and bifidobacterial isolates for phenotypic resistance with microdilution method. At microdilution test 14 out of 104 strains showed resistance against antibiotics, nine strains against erythromycin, four strains against tetracycline and one strain against kanamycin. Those 14 strains with high MIC were later on screened with PCR to see if they contain any of resistance genes. Out of 14 strains that showed phenotypic resistance we discovered that one strain of B. longum (34-7) carries gene for erythromycin resistance erm(B) in his DNA, one strain of B. adolescetnis (IM677) carries gene for tetracycline resistance tet(O), strain B. longum (34-8) carries gene tet(W). None of the strains tested carried genes for resistance against kanamycine.