Because of their attractive photoelectrical properties, perovskite-phase, CsPbX3 (X = I, Br, or Cl) materials have recently gained attention for their applications in resistive switching (RS) memories. However, phase transition of the CsPbI3 from perovskite (cubic phase) to nonperovskite (orthorhombic phase) at room temperature is problematic; it remains a challenge to apply nonperovskite CsPbI3 in RS memories. In the present work, a polymethylmethacrylate (PMMA)-assisted deposition method for nonperovskite CsPbI3 is introduced to fabricate a composite film of CsPbI3 with PMMA (PMMA@CsPbI3) with a smooth surface morphology on fluorine-doped tin oxide (FTO) substrates. Devices with a Ag/PMMA@CsPbI3/FTO architecture show nonvolatile RS characteristics with an ON/OFF ratio around 102, endurance over 500 cycles, and a retention time of 103 s. Analyses suggested that a Schottky barrier at the Ag/PMMA@CsPbI3 interface and a bias-induced migration of Ag ions within the composite films are responsible for the RS operation. This is the first record for RS devices based on nonperovskite CsPbI3, and it may bring the future research on nonperovskite CsPbI3 applied in RS memory devices some new inspiration..