Abstract <p>The article describes the results of experimental studies on diffusion welding under conditions of hot isostatic pressing with preliminary heat treatment of the surface of workpieces made of a number of steels and alloys by nanosecond pulses of laser ultraviolet radiation. Estimates of the characteristics of laser radiation and the parameters of the modified surface layer due to its melting by a laser pulse are given. It is shown that the processing of samples from a heat-resistant nickel-based alloy CrNi55MoWZr by a scanning beam of nanosecond laser pulses with a wavelength of 355 nm, a duration of 10 ns, and an energy density of 2 J/cm², following at a frequency of 100 Hz, improved the mechanical properties of the weld. The ultimate strength increased by 10%, and the elongation increased by 20%. In addition, the use of a laser made it possible to reduce the temperature of the diffusion welding process by 160°C while maintaining the mechanical properties of the welded joint. The most probable reason for the improvement of the properties of the welded joint was the appearance of low-temperature superplasticity caused by the formation of a fine-grained surface structure because of preliminary laser processing of workpieces.</p>