On the basis of energy distribution in the region from 6800 to 8400 Å, we determined spectral types (M4—M6) and values of effective temperature T_eff (2700—2900 K) and acceleration of gravity lgg (4.0—4.5) for five M-dwarfs. The stellar spectra were obtained on the Walter Baade Telescope (6.5 m, the ESO) with the help of the complex IMACS with the resolution R = 4000. We performed spectral classification based on the spectral indices and estimated effective temperatures of the stars using the spectral types. The values of T_eff and lg g were determined by comparing the observed and theoretical energy distributions. Synthetic spectra were calculated both for the dust-free atmosphere model of red dwarfs (NextGen) and for the semi-empirical atmosphere model of Pavlenko et al. The semi-empirical atmosphere model takes into account the effect of the dust presence in stellar atmospheres. We calculated dust parameters for each star and demonstrated the necessity of considering the effect of a decrease in the concentration of TiO molecules due to their condensation on dust grains for T_eff < 3000 K. We concluded that the scattering of radiation by dust particles scarcely affects the energy distribution for spectra of the stars considered.