We studied the magnetic structure of a chiral magnet DyNi 3 Al 9 , with T N = 8.5 K, by single crystal neutron diffraction. The RNi 3 Al 9 (R = rare-earth) system has recently been studied systematically from the viewpoint of chiral magnetism in the space group R32, allowing left and right handed crystal structures. We found that the magnetic order is described by the propagation vector q=(0, 0, 0), i.e., the unit cell of magnetic and crystal structures are identical. By combining the information from magnetization and magnetic susceptibility, it is inferred that the ordered moments lie in the cplane in an almost antiferromagnetic arrangement with small ferromagnetic component by canting. The result of structural analysis by X-ray diffraction is also reported.