Anaplasmataceae is part of a family of small intracellular proteobacteria which includes the genera Anaplasma, Ehrlichia, Neorickettsia, Wolbachia, Aegyptianella and Candidatus Neoehrlihia. These bacteria survive as endosymbionts in other cells, but at the same time can cause diseases in humans and animals. Bacteria of the genus Anaplasma are transmitted by vectors (ticks), and the most important in Europe is the tick species Ixodes ricinus. Species of family Anaplasmataceae are complicated to grow in cell cultures as well as to prove them in clinical samples by different coloring, therefore the research is based on molecular methods. This thesis analyzed the samples of DNA isolated from the blood of dogs belonging to the archives of the Laboratory of parasitology of the Croatian veterinary institute. DNA was amplified by polymerase chain reaction "nested" protocol, 16S rRNA gene parts sequenced and analyzed in the appropriate programs. As there are no data on the species present in Croatia the goal was to investigate which species of the genus Anaplasmataceae are present in dogs from Croatia and to determine the frequency of certain species. From a total of 68 samples of dogs in 22 of them the DNA of bacteria from the family Anaplasmataceae was found. The most abundant species was A. Platys (64 %) and species A. phagocytophilum (18 %) and Wolbachia, endosimbiont of Dirofilaria repens (18 %) also were found.