Dispersion strengthening behaviour of zirconium-based alloys of the Zr–1.5Sn–1Nb system containing nanoparticles of ZrO$_2$ (less than 5 nm) is studied in the as-cast (after electro-arc melting) and wrought conditions using X-ray photoelectron spectroscopy, electron microscopy as well as constant-rate tensile tests and differential-stress creep experiments. The obtained results indicate that nanostrengthened alloys at 673 K are more creep resistant than their age-hardened and precipitation strengthening counterparts. Their features have substantial desirable improvements in creep resistance and long-term strength with increasing of ZrO$_2$-nanoparticles’ concentration in a range from 0.3% to 1.2% due to the greater thermal resistance of their heterogeneous structure. The most probable mechanism of nanodispersion strengthening is assumed similar to known one as thermally activated detachment of interfacial dislocations from dispersoids according to current theoretical Rosler–Azrt–Wilkinson concept. These results could be useful for manufacturing the fuel elements (clad tubes) for the nuclear power engineering.