We have demonstrated that a two-dimensional photonic crystal fiber can be used as a novel nonlinear medium for atom optical experiments. Our results show for the first time that cold atoms can be guided optically through this fiber with high efficiency and especially with a high density. In order to study this system a new experiment for creating cold optically guided atoms has been built up. Our results show that the experimental parameters governing the atomic flux are in a good agreement with a self-developed numerical model as well as with other theoretical predictions.