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Encounter of the solar system with galactic molecular clouds produce significant distortion of the Oort cloud. We have found an excitation of density waves in the Oort cloud under the effect of encounter with molecular cloud. We take a molecular cloud as a test particle with the mass M=5$x$10$^5$ solar mass and the distance of the closest approach P=20 pc. This perturber excites one-armed spiral density wave if it moves in the ecliptic plane in a retrogade orbit. It excites two-armed spiral density wave if it moves in the ecliptic plane in a prograde orbit. Two- armed spiral density wave is excited also when molecular cloud movement is perpendicular to the ecliptic plane. Density waves were excited in the Oort cloud when initial cometary orbits were situated near the ecliptic plane and their eccentrisities were e<0.968. A rotating bar-like structure arises when the initial cometary orbits are elongated enough. Both density waves and bar-like structures in the Oort cloud are destroyed after passages of galactic molecular clouds.
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