The velocity profiles in the laminar free convection boundary layer on a uniformly heated vertical plate are measured by a Laser Doppler Velocimeter for air in the range of modified Grashof number G $r_{chi}$*=1.172x10$^{9}$ . The fringe mode, forward scatter type of the LDV system is used and the small magnesium oxide particles are used for the scattering pafticles. The analytical non-dimensionalized velocity profiles are obtained by use of an analog computer for the comparison with the experimental results. The experimental reults are in good agreement with the analytical solution obtained with an aid of the analog computer.er.