Soot production has been studied in axisymmetric turbulent diffusion flames of methane, ethylene and propane. Soot volume fraction has been measured by the extinction technique. The vertical component of the velocity has been obtained by Laser Doppler Velocimetry. The soot mass how rate has been determined through flame sections to study global production of soot in flame zones. This rate reaches a maximum value between 0,5Lf and 0,75 Lf (Lf being the visible length of the flame). The characteristic soot volume fraction obtained from extinction optical depth can be used to determine the soot mass how rate.