Magnetic alignment of columnar discotic liquid crystals (DLCs) on a substrate by solvent-evaporation under a field has been investigated using small angle neutron scattering (SANS). DLC solutions normally form randomly oriented columnar structures on substrates during spin coating or drop-casting processes. The controlled orientation of the columnar structures, however, is crucial for the DLC-based electronic devices. In this study, a 4 wt% cobalt 2, 3, 7, 8, 12, 13, 17, 18-octakis (n-decylthio) porphyrazine (CoS10) in hexane was drop-casted onto a quartz plate under an applied magnetic field (H=0.7 T) which lies on the substrate plane. The SANS pattern of the casted CoS10 showed strong anisotropy, which clearly indicates that the columnar directors of CoS10 align perpendicular to the applied magnetic field. The new method presented here may open a simple and easy solution process to fabricate aligned columnar DLC on substrates.