The characteristics of soot particles formed during combustion of liquid hydrocarbons in a laboratory model of an original burner with injection of a superheated steam jet into the reaction zone are experimentally studied. The concentration and size distribution of soot particles formed in the burner flame are measured by a diffusion aerosol spectrometer. It is shown that the majority of the primary particles have sizes ranging from 20 to 60 nm. The particle concentration in the external flame rapidly decreases with distance from the burner exit from 108 to 5 · 106 cm−3. The images obtained by transmission electron microscopy demonstrate a chain-branched (fractallike) structure of aggregates. The primary particles composing these aggregates have a union-like structure with the interplane distance between the layers smaller than 1 nm. Compact aggregates with sizes up to 500 nm are observed in cooled combustion products. The content of soot in combustion products is 35 mg/m3, and the mean particle mass is 7 · 10−12 mg. Results obtained in the combustion modes with injection of a superheated steam jet and with injection of an air jet are compared.