Nanometer-sized crystallites of Y-type strontium hexaferrite, Sr2Ni2Fe12O22 and its Mn- and Cr-doped derivatives have been synthesized by the sol-gel method. Y-type phase formation was achieved at a considerably lower temperature of 950 degrees C than is required in the traditional solid-state method (1200 degrees C). The effect of doping of manganese at the tetrahedral site, Sr2Ni2-xMnx Fe12O22 (x = 0.0-2.0), and chromium at octahedral site, Sr2Ni2Fe12-yCryO22 (y = 0.0-1.5), has been studied. The crystal structure remains unaffected by the substitutions. The crystallite size in the range of 13-45 nm is calculated from the X-ray diffraction data. The energy-dispersive X-ray fluorescence analysis shows that Y-type hexaferrites can be prepared with a base of strontium. The extent of doped Cr-13 ions at the octahedral site has been increased from the reported maximum value of y = 1.5. Scanning electron micrographs of the samples showed a homogenous microstructure. The dc electrical resistivity studies show that these hexaferrites exhibit high resistivity at room temperature. Cr-doped samples have comparatively higher resistivity than Mn-doped samples. The doubly doped (Cr+Mn) samples possess high resistivity (7.37 x 10(9) Omega-cm), a low dielectric constant (33.88 at 3000 Hz), and a high Curie temperature (>698 K). The dielectric energy losses are minimized by increasing the Mn and Cr contents of the synthesized samples.