Abstract New multifunctional artificial synaptic devices, which are capable of sensing various external information in addition to electrical stimuli and processing multiple signals in parallel in the same way biological synapses do, are in urgent need. Recently, several optical memristors are proposed to simulate photosynaptic plasticity for neuromorphic computing. Here, a light‐responsive memristor is described based on Cs 0.05 (FA x MA 1− x ) 0.95 PbI y Br 3− y (CsFAMAPbIBr), a kind of organometal trihalide perovskite (OTP) with outstanding photovoltaic properties and stability. Such a memristor with Al/CsFAMAPbIBr/SnO 2 doped with fluorine(SnO 2 :F) structure exhibits notable resistive switching (RS) behavior, which is the basic characteristic for further implementing complex synaptic plasticity. Analysis suggests that the RS characteristic origins from intrinsic ion migration within the OTP layer, which modulates the Schottky barrier at the CsFAMAPbIBr/electrode interface. Moreover, the memristive characteristics of the devices can also be modified by reshaping the stacking devices’ architecture or by applying light stimuli. This work elaborates the correlation between RS behavior and the ion migration of OTP and provides insights on the light‐responsive memristive mechanism of the memristor based on CsFAMAPbIBr.