Ferromagnetic resonance (FMR) experiments on non-interacting maghemite (γ-Fe 2 O 3 ) nanoparticles in ferrofluids, are performed in X- and Q-bands as a function of the particle diameter (4.8-10nm) and the temperature (3.5-300K). The colloidal stability and grain size are controlled through a chemical synthesis, the polydispersity being reduced by a phase separation method. The dependencies of spectral characteristics with temperature T, particle volume V and experimental frequency ω, reveal a generic behavior of the FMR lines due to the effect of thermal fluctuations. Their scaling with the Langevin parameter ξ 0 =MVω/γk B T is explained in the framework of the theory of FMR for an assembly of independent single-domain anisotropic particles.