Dy3+ and Y3+ ions co-doped Zn0.5Mn0.5Fe2O4 (ZMDyYFe) (x = 0.0 0-0.05) nanospinel ferrite nanoparticles (SFNPs) have been synthesized through an ultrasonication approach. The rare earth co-doping with Dy3+ and Y3+ ions was applied to tune the structural and magnetic properties of the ZnMn spinel ferrites. The influence of the co-doped of both Dy3+ and Y3+ ions on the structural, optical, and magnetic characteristics of Zn0.5Mn0.5Fe2O4 SFNPs was analyzed in detail by X-ray diffractometry (XRD), scanning electron microscopy (SEM), high-resolution tunneling electron microscopy (HR-TEM), energy dispersive X-ray analysis (EDX), and elemental mappings. XRD results revealed the formation of the spinel phases and the structural changes which were accompanied the Dy3+ and Y3+ ions co-doping. The cubic spinel phase of all samples has been confirmed by the application of Rietveld refinement. As the value of "x" increased up to x = 0.04, the lattice constant was found to increase from 8.401 to 8.408 angstrom and the size of the crystallites was calculated to be in the range 7.26 nm-11.10 nm. HR-SEM and HR-TEM micrographs also presented the cubic morphology of the products. Diffuse reflectance spectroscopy (DRS) measurements were done on pure and Dy3+ and Y3+ co-doped Mn0.5Zn0.5Fe2O4 SFNPs. Direct band gaps (E-g) were extracted from Tauc plots. E-g values existed in a narrow range between 1.64 eV and 1.74 eV. Magnetic investigations exhibited the superparamagnetic behavior at RT (room temperature) and ferrimagnetic behavior at 10 K for synthesized samples. At RT analyzes, undoped Mn0.5Zn0.5Fe2O4 SFNPs had the maximum saturation magnetization (M-S) of 34.84 emu/g and magneton number (n(B)) of 1.47 mu(B) . An inverse proportion with the increasing ion ratio were observed among those parameters. The 10 K magnetization data revealed that co-doped Mn0.5Zn0.5Dy0.02Y0.02Fe1.96O4 SFNPs had magnetic parameters of M-S,M-max = 67.39 emu/g, n(B,max) = 2.88 mu(B) and H-C,H-max = 574 Oe (HC: coercivity and max: maximum). Among the rest of the co-doped samples, MS and nB data had a similar negative trend with respect to the increasing ion ratio including the remnant magnetizations (M-r). The rest of the H-C values were found to be between 275 Oe and 361 Oe. Squareness ratios (SQRs= Mr/MS) had a range of 0.181-0.321 and confirmed the multi-domain wall structure for all SFNPs at 10 K. The maximum value of effective crystal anisotropy constant (K-eff) 6.04 x 10(-4) Erg(g belongs to Mn0.5Zn0.5Dy0.02Y0.02Fe1.96O4 SFNPs, and others have the same order of 10 4 Erg(g for Keff constants. Although this sample has the largest internal anisotropy field (Ha) of 1794 Oe, it can also be classified as a soft magnetic material like other nanoparticle samples. The Dy3+ and Y3+ ions co-doped ZMDyYFe (x = 0.00-0.