The goals of this work are to obtain and to study the structure and properties of chitosan fibers filled with chitin nanofibrils. Biocompatible and bioresorbable composite fibers consisting of chitosan filled with anisotropic chitin nanoparticles (nanofibrils) were prepared by the coagulation method. The structure of the fibers and of the chitin nanofibrils was investigated by the XRD and SEM methods. Chitin powder was obtained by lyophilization of inition chitin suspension, films by drying the aqueous suspension. It was evident that the microparticles have strip type structure with the transverse size approximately 30 μm and with the thickness of 0.1 μm; they consist of nanofibrils of 11-12 nm width and 600-800 nm length. The chitin nanofibrils were used as the filler for obtaining the bioresorbable composite fibers. The results of rheological studies allow to conclude that the dependence of the viscosity (η) on the shear rate (γ) has nonlinear behavior for all investigated solutions. For the chitosan solution not containing the filler, the decrease of viscosity was observed at the shear rate of 10 s-1 or more. The threshold value of the shear rate at which the dependence η(γ) becomes nonlinear displaces to the smaller values when the chitin nanofibril content increases. For the mixture containing 20 wt% of chitin filler the dependence η(γ) becomes linear over a wide range of shear rates. It was found that both components (chitin and chitosan) of these composite fibers were oriented. The incorporation of 0.1–0.3 wt.% of chitin nanofibrils (with respect to dry chitosan) into the chitosan matrix led to an increase in strength and Young modulus of composite fibers. Based on these results, a scheme of formation of oriented structure of composite fibers comprising anisodiametric nanoparticles was developed. The adhesion of stem or somatical cells on the material surface is one of the basic criteria of its use as the matrices for the cellular technologies. SEM micrograph of the chitosan fibers taken after the cultivation of stem cells on them indicated that the surface of the fibers contained stem cells, which were well-fixed and split. The fibrillation of the fibers, obtained on high degree of drawing, contributed to the adhesion on fiber surface of the mesenchymal stem cells that changed their form.