The fabrication of memory devices based on the Ag/PMMA:Na/Ag structure and their electrical characteristics are reported. The Ag/PMMA:Na/Ag devices show a hysteresis behavior with different Na contents. The most evident hysteresis behavior for memory effect, represented as the on/off current ratio, is found to be as high as 105 in Ag/PMMA:Na-180s/Ag devices. The carrier conduction mechanisms between the high and low resistance states and the transition states are further examined on the basis of trap-assisted space charge limited current theory. Such devices sustain at least 60 operation iterations and 100s duration tests. Hence, the idea of incorporating Na particles into the organic layer of memory devices creates a promising direction for the development of organic memory devices.