Structural, magnetic, and dielectric features of Tm-Tb ions co-substituted Sr hexaferrites (HFs) contrived via citrate sol-gel approach were investigated. Rietveld analysis of XRD patterns proved the existence of the hexagonal ferrite structure. The size and morphology were examined by XRD, SEM, and TEM techniques. The electrical and dielectric belong to Tm-Tb co-substituted Sr-HFs were extensively explored with temperature, frequency, and substitution ratio using the complex impedance spectroscopy technique. It was found that Tm-Tb substitution has a strong influence on the dielectric loss, dielectric constant, ac/dc conductivity and dissipation factor. It was observed that activation energy levels can be changed to a certain level with co-substitution ratio. Measurements of magnetization against temperature M(T) and AC magnetic susceptibility were also performed. The investigation of M(T) experiments showed ferrimagnetic behavior between 10 and 325 K and a super-spin glass-like demeanor was found at very low temperatures. Vogel-Fulcher, Neel-Arrhenius and critical slowing down models were considered to explain the AC susceptibility results. The examination of AC susceptibility disclosed a strengthening of magnetic exchange interactions with Tb3+ and Tm3+ substitutions.