The non-catalytic hydrovisbreaking of straight-run mazut residue in an upflow reactor filled with inert turbulizer-packing having a cellular structure and a free volume of about 65% was investigated. Feedstock conversion of 55.1 % was obtained under moderate conditions for such a process (temperature 450 degrees C, hydrogen pressure 5 MPa). The conversion of the non-volatile residue, boiling above 540 degrees C, amounted to 90 % with 96 % demetallization and up to 76% conversion of asphaltenes and tars.. The main product of the hydrovisbreaking process was a kerosene-gasoil fraction with a yield of 43.6%. The distillate products of hydrovisbreaking were similar in quality to the distillates of a slow coking process, except for the lower sulfur content and the complete absence of silicon. The unconverted residue obtained after removal of the light distillates at atmospheric pressure had low viscosity and a low pour point. It can be used as feedstock in hydro purification for marine fuel production.