The main objective of this study was to investigate the effects of annealing temperatures ranging from 500 °C to 550 °C on spray pyrolysis technique Bi2Fe4O9 thin films. The presence of no intermediate impurity phases in the Bi2Fe4O9 sample was confirmed by X-ray diffraction (XRD), which indicates that the phase is typical orthorhombic with Pbnm space group. According to Scherer's equation, the average crystallite sizes were determined to be 23 nm. Atomic force microscopy (AFM) demonstrated that Bi2Fe4O9 NPs are symmetrically dispersed nanorods with a topographic shape on the films' surface.An increase in annealing temperature causes the surface roughness to increase from around 6.76 nm to 8.67 nm, indicating a modification in the thin film's crystal structure. After observation, the fractal dimension values were determined to be 1.78 and 2.06. It is evident that the fractal dimension increases as the annealing temperature rises, from 500 °C to 550 °C, respectively. This finding suggests that can be used to characterize how the whole grain shape varies along the growth direction. Furthermore, the fractal dimension has spatial and profile deviation information, in contrast to RMS roughness.