The influence of the parameters of plastic deformation by ultrasonic burnishing during finishing treatment on the surface roughness of workpieces made of Р6М5 and 9ХС steels with an initial surface hardness of 57¸60 HRC is investigated. The D-optimal Hartley—Kono plan was used in the experiments for four factors (workpiece rotation frequency, feed, loading force, ultrasound power). Keywords: ultrasonic finishing, indenter, ultrasound power, surface roughness, plastic deformation zone. v.slutskov@narfu.ru