The article presents materials on use of ultrasonic waves to reduce the smoke and toxicity of diesel engine exhaust gases. The results of the experiments are presented. The hypothesis on the reduction of smoke and toxicity of the exhaust gas due to the acceleration of the coagulation of its particles under the action of ultrasound has been confirmed. The dependences of the degree of turbidity of a diesel car on the number of revolutions of the engine crankshaft per minute and the dependence of the content of harmful impurities in the exhaust gases, without exposure and under the influence of ultrasound, at various revolutions of the engine crankshaft per minute, have been obtained. In addition, graphs of the amount of settled soot in an ultrasonic device on the number of engine revolutions per minute were obtained experimentally without and under the influence of ultrasound.