Biopolymer-based memory devices have a multitude of potential applications in biomedical research. In this paper, we demonstrate the tunable memory behavior of the chitosan (CS) based memory devices as a function of CS thickness using the device structure of ITO/CS/Cu. Also, a clear distinction between filamentary and interfacial resistive switching was witnessed. High on/off ratios of 1870 and 1280 were observed in the filamentary resistive switching (for CS thickness of 80 nm) and interfacial resistive switching (for CS thickness of 200 nm) modes, respectively. The switching mechanism has also been analyzed using linear fit analysis and attributed to the formation and rupture of the conducting filaments, and charge accumulation at the metal/CS interface. This study opens up the possibility of developing write-once-read-many and read-and-write (RWM) random access memory devices. © 2021 IOP Publishing Ltd.