The structural and optical properties, as well as dielectric characteristics at various frequencies (0.1 Hz—20 MHz) and temperatures, T (300–400 K), of hydrothermally synthesized SnO2 nanoparticles, Cu/SnO2, and Fe/SnO2 composites have been investigated. The crystal structure is mostly formed of a tetragonal SnO2 phase, with a second phase of monoclinic CuO or rhombohedral Fe2O3 detected in Cu/SnO2, and Fe/SnO2 composites, respectively. The direct optical band gap, residual dielectric constant, and density of charge carriers are increased, while ac conductivity (σ ac) and dielectric constant decreased in Cu/SnO2 and Fe/SnO2. The value of σ ac was decreased while the electric Q-factor was increased by increasing T. SnO2 obeyed the hole-conduction mechanism for 400 ≥ T (K) ≥ 300, while Cu/SnO2 and Fe/SnO2 obeyed the electronic-conduction mechanism for 400 ≥ T (K) > 300. The binding energy is independent of T for SnO2, whereas it increases with rising T for Cu/SnO2 and Fe/SnO2 composites. F-factor and electronic polarizability are improved by a rise of T for SnO2 and Cu/SnO2 meanwhile are decreased for Fe/SnO2. The electrical impedance of the grains and their boundaries as well as equivalent capacitance are increased by increasing T and have higher values for Fe/SnO2 at T > 300 K. The obtained results recommend the synthesized Cu/SnO2 and Fe/SnO2 composites to be used as catalysts for water purification, anodes for lithium batteries, supercapacitors, and solar cell applications amongst others.