Single-phase SrGdxFe12-xO19 (x = 0.00-0.05) nanosized M-type hexagonal ferrites (NHFs) were prepared via citrate sol-gel route. The formation of Gd substituted Sr-hexaferrites has been confirmed by XRD, SEM, TEM and EDX for all substitutions. The X-ray powder patterns revealed the hexagonal crystal structure of all products. The electrical and dielectric properties of SrGdxFe12-xO19 NHFs were investigated extensively with an impedance spectroscopy up to 3.0 MHz from 20 to 120 degrees C. Both electrical and dielectric components including ac/dc conductivity, dielectric constant, dielectric loss and lossy tangent were evaluated for measurement temperatures up to 120 degrees C. It has been indicated that ac conductivity generally complies with power law rules, mainly dependent on Gd3+-ion substitution ratios. The impedance analysis showed that due to the influence of various Gd3+-ion substitution ratios in the NHFs, the conduction mechanisms can mainly be attributed to the grain-grain boundaries. The dielectric constant of SrGdxFe12-xO19 NHFs owns a normal dielectric distribution with the frequency, largely due to varying substitution ratios. In other words, the variation of Gd3+-ion substitution can be used to modify the conduction mechanism of NHFs. Therefore, the observed change in dielectric properties as a function of frequency can be clarified on a phenomenological basis by Koop's model of the electrical conduction mechanism in most composite ferrites.