A diffusion flame at a low flow rate of propane gas in still air was surrounded by a circular mesh electrode. A circular burner of 8 mm diameter was used as the other electrode. Alternating electric field of high frequency and high voltage was applied between these electrodes. The luminosity which radiated from high temperature soot particles was measured by a photomultiplier. The oscillating frequency of the luminosity changed proportionally up to 80 Hz with the frequency of the applied electric field. The electrical mobility and effective equivalence diameter of soot particles in the flame were estimated by means of the displacement of the luminous signal and the relaxation time of the soot particles. Average values were calculated to be about 0.15 m2/(V·s) and 40 μm respectively. The deformation of diffusion flames at low flow rate has been investigated numerically by the use of a rectangular nozzle in magnetic field. The deformation of the flame was independent of the direction of the magnetic field. The strength of the external force by the magnetic field was proportional to the value of two powers of magnetic field (=H2) . The force exerted upon the boundary between the flame and the air by the magnetic field was one induced by the difference of the volumetric susceptibility between the two gases. The deformation, tilt and turn of the flame are caused by the buoyancy and the induced force by the magnetic field. The numerical analysis of the turn of the flame was conducted using the value of the pressure difference at the boundary between the two gases.