Gelation chemistry and the related phase development play important roles in chemical solution-derived ferroelectric oxide thin films. Here, we report a detailed study on the gelation chemistry behavior of sol–gel Sm-doped bismuth ferrite (Bi1–xSmxFeO3–BSFO) thin films. The precursor solutions were first investigated to elucidate the role of Sm dopant on film molecular networks. The hydrolysis and esterification reactions were found to be dependent on the metal cation species; compared to Bi3+ and Fe3+, the introduction of Sm3+ accelerates the esterification reaction. The subsequent crystallization process of deposited BSFO films was further analyzed to understand the phase structure development as a function of Sm dopant concentration and heating temperature. (00l)-oriented BSFO phases were observed in all films. With the increase of the Sm dopant, the paraelectric orthorhombic (O) phase and antipolar phase start to form at x = 0.10. The domain structure and ferroelectric properties show a concomitant dependence on the Sm doping component. Upon increasing the Sm doping component, the virgin domain amplitude decreases, while the poled domains show an enhanced amplitude. The amplitude variation between the unpoled and poled domains is as high as 760% at x = 0.10. The ferroelectric properties of BSFO films are greatly improved due to the Sm doping. At x = 0.14, a fully developed polarization hysteresis loop is acquired. With the further increase of Sm composition to 0.15, a slightly distorted loop, which indicates an electric-field-induced paraelectric O phase to ferroelectric R phase transition, is first observed in chemical solution deposition (CSD)-derived BSFO films. These results provide a deep insight into the development of rare-earth-doped BFO films through a commercially viable chemical solution method.