The objective of this research was to study the change of Mn mole fraction to the structure and magnetic properties of GaN:Mn thin film by sol-gel method. A thin film ferromagnetic semiconductor of GaN:Mn has been deposited on Si(111) substrate by using Chemical Solution Deposition method (CSD) and spin coating technique. Atomic composition, crystal structure, morphology and magnetic properties of the GaN:Mn thin film were characterized using Energy dispersive of X-ray (EDX), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Scanning Probe Microscopy (SPM) and Vibrating Sample Magnetometer (VSM). The results showed that the GaN:Mn thin film still contains carbon atom impurity and non-stochiometri. The GaN:Mn thin film has polycrystalline form in which the 2θ angle of GaN peaks have been shifted (~ 0.22o) for that with Mn composition of 5.24% at 32.62° angle. SEM and SPM investigation show the surface of GaN:Mn thin film with 6% Mn distributed by homogeneous grains and the level of surface roughness was 15.3 to 29.90 nm. However, the other magnetic phases (Ga5.2Mn) and oxide phases of Mn, Si and Ga were also detected in the GaN:Mn thin films. Sample with 7.43% Mn exhibits optimum composition results in appearance of ferromagnetic properties. The remanent magnetic (Mr) and saturation magnetic (Ms) of sample were achieved at 5.04 emu/cm3 and 91.5 emu/cm3, respectively.