The given paper investigates the frequency dependence of the interband and intersubband absorption coefficients of weak electromagnetic wave (EMW) in the quantum wires in a uniform magnetic field, which is directed perpendicular to the axis of the nanostructure. It is assumed that a quantum wire is oriented along the OX-axis, and the magnetic field is directed along the OZ-axis. The calculations were performed for the quantum wire in a parabolic potential model on the base of the general relations of the non-equilibrium quantum statistics. Eventually, using the Kubo‘s formula, the expressions for these light absorption coefficients were obtained, taking into account the elastic scattering of the charge carriers (electrons and holes) on the long-wavelength acoustic vibrations. On the basis of the derived expressions the features of changes in the light absorption spectra for the interband and intersubband electron transitions were studied in detail at the variations of the magnetic field value H in a fairly wide range. It is shown, that the frequency dependence of the interband light absorption coefficient consists from the peaks corresponding to the individual interband optical transitions. The distance between the optical bands (peaks) is determined not only by the magnetic field value, but also by the quantum wire radius (R0): it increases with growth H and decreases at increasing R0. Each of these peaks is described by a bell-shaped curve, and its form and half-width are determined by the interaction of the charge carriers with phonons. The form of a separate peak is asymmetric – with sharp rise in the long-wavelength wing and smooth downturn in the short wing. At increasing of the magnetic field value the half-width of each peak is increased. In particular, it was considered the electron optical transition from the quantized state with n' + m' = 1 in the valence band to the quantized state with n + m = 1 in the conduction band (n', m' and n, m, – the quantum numbers that describe the states of the charge carriers in the respective band of the quantum wire). It is shown, that at increasing H the absorption peak is shifted toward the higher frequencies and is split into two peaks, and the magnitude of this splitting appreciably depends on the magnetic field, so that it increases with growth H. It is also shown, that in the magnetic field the optical properties of the quantum wires associated with electron transitions between the quantized levels in the conduction band (intersubband transitions) depend on the polarization of the absorbed EMW. In particular, the calculations show that for the x-polarized EMW (i.e., the linearly polarized light with polarization vector, which is directed along the axis of the quantum wire, extends perpendicular to this axis), a new absorption channel is appeared, owing to an influence of the magnetic field. Herewith, the frequency dependence of the intersubband light absorption has the form of a symmetrical curve, and its halfwidth increases at increasing H. Also, the features of the intersubband light absorption, taking place in the magnetic field, are investigated for the cases of the y- and z-polarized EMWs. It should be noted, that the light absorption coefficients (both interband and intersubband), which were studied as the functions of the EMW frequency, also noticeably depend on the value of such parameter as the radius of the quantum wire.