The invention relates to a process for preparing nitroalkanes by reaction of at least one alkane with at least one nitrating agent in the gas phase, wherein the nitration is carried out in a microstructured reaction zone having parallel channels having hydraulic diameters of less than 2.5 mm and a total specific internal surface area of more than 1600 m2/m3 and the alkane and the nitrating agent are conveyed under a pressure of from 1 bar to 20 bar through the reaction zone and reacted at a temperature of from 150° C. to 650° C. and the reaction products are cooled downstream of the reaction zone and discharged and the at least one nitrating agent is introduced over from two to ten introduction points along the reaction zone.