Solar occultation observations of the Martian atmosphere from the Phobos spacecraft resulted in nine vertical profiles of volume extinction coefficient at 3.7 and (1.9 \mu \mathrm{m}) in the altitude range of 12-35 km. Interpretation of the profiles in terms of the Mie scattering theory, with the adopted refraction index 1.5-0.01 (i) and particle size distribution of gamma-type, gives vertical profiles of the particle number density and the effective radius (weighted-mean extinction cross-section). The number density ((n)) is found to be typically (0.2-1 \mathrm{~cm}^{-3}) between 15 and (25 \mathrm{~km}); the effective radius (\left(r_{\text {eff }}\right)) varies from (0.8 \mu \mathrm{m}) near (25 \mathrm{~km}) to (1.6 \mu \mathrm{m}) at (15 \mathrm{~km}). Average values of these parameters are (n=0.32 \pm 0.15 \mathrm{~cm}^{-3}) and (r_{\text {eff }}=1.26 \pm) (0.2 \mu \mathrm{m}). The dependence of these parameters on the refraction index and an effective variance of the size distribution is also studied. The data can be interpreted by a one-dimensional dynamic atmospheric model with a source of aerosol of (3 \cdot 10^{-12} \mathrm{~g} / \mathrm{cm}^{2} / \mathrm{sec}) near (22 \mathrm{~km}). The derived mixing coefficient, (K=(1.1 \pm 0.5) \cdot 10^{6}) (\mathrm{cm}^{2} / \mathrm{sec}) found to be independent of height between (15 \mathrm{~km}) and 30 (\mathrm{km}\left(d \log K / d z \leq 0.025 \mathrm{~km}^{-1}\right)). The width of the particle size distribution, (\nu_{\text {eff }}), is estimated with the modeling from the vertical profiles of particle number density assuming it is independent on height: (\boldsymbol{\nu}_{\text {eff }}=\mathbf{0 . 2} \pm \mathbf{0 . 1}). Mean value of the total optical thickness obtained by extrapolation of the extinction profiles to the surface, assuming dust scale height equal to that of gas, is (0.24 \pm 0.06) at (1.9 \mu \mathrm{m}). O 1993 Acadernic Press, Inc.