In this study, structure, optical character, morphology, element-valence and characteristic ferroelectricity of BiFeO3 (BFO) and BiFe0.96Al0.04O3 (BFAO) thin films were investigated experimentally. BFO and BFAO thin films were prepared on fluorine-doped tin oxide (FTO) substrates via spin coating with two acid solvents. One solvent was aqueous solution of nitric acid (solvent Ⅰ), and the other one was mixture of 2-methoxyethanol and glacial acetic acid (solvent Ⅱ). X-ray diffraction (XRD) showed that films maintained their rhombic perovskite structures, which were R3c. Raman spectra showed that Al doping causes structural distortion. Al doping solves the problem of porosity and improves the density of BFO film. Average grain size of BFAO-Ⅱ sample is about 110 nm, and, its thickness is the smallest (~714 nm). This indicates that BFAO-Ⅱ sample is highly compact. Energy spectrum shows that Al has doped in the film, uniformly. X-ray photoelectron spectroscopy (XPS) shows that the presence of Al inhibited the floating of Fe valence. BFAO-Ⅱ sample has excellent ferroelectricity (2Pr ~ 110 μC/cm2), and leakage current density (~ 10-2 A/cm2) is lower than that of undoped BFO film. Al doping can reduce the band gap width (Eg) of BFO films, specifically, values of Eg are 2.28 (BFO-Ⅰ), 2.26 (BFO-Ⅱ), 2.17 (BFAO-Ⅰ) and 2.21 (BFAO-Ⅱ) eV. This work provides new idea for the application of Al-doped BFO films in photocatalysis and photovoltaic devices.