La-Y substituted Ni-Cu-Zn nanospinel ferrites (NSFs) having the following formula Ni0.3Cu0.3Zn0.4LaxYxFe2-2xO4 (x = 0.0-0.10) were fabricated prepared by ultrasonic irradiation approach. The X-ray powder diffractometer (XRD), scanning electron microscope (SEM) and Fourier-transform infrared spectroscopy (FT-IR) were utilized to analyze the structure, vibration bands and morphology. The impedance spectroscopy technique was used for the analysis of electrical and dielectric properties of La3+ and Y3+ ions co-substituted Ni0.3Cu0.3Zn0.4Fe2O4 NSFs. Some important parameters such as ac conductivity, activation energy, dielectric constant and dielectric loss were examined as functions of frequencies and temperatures for a variety of La and Y co-substitution ratios. In general, ac conductivity is observed to fluctuate slightly with the elevated temperatures while its fluctuation level decreases somehow with an increase in co-substitution ratios. Furthermore, the frequency dependence of dielectric functions could be described by Koop's models based on Maxwell-Wagner theory, which elucidates the correlation between the polarizability coefficient and dielectric constant in inhomogeneous double-layer structures.