A fundamental component of episodic memory is memory for the temporal order of items within an episode. Convergent evidence suggests that both the medial temporal lobe (MTL) and the prefrontal cortex (PFC) contribute to temporal order memory. Previous physiological studies examined neuronal properties in MTL (Naya & Suzuki, 2011) and PFC (Ninokura et al., 2003 & 2004; Warden & Miller, 2007). However, no studies had yet compared the two brain regions directly. In order to characterize their contributions to temporal-order memory, we recorded single-unit activity from PFC and MTL in two macaque monkeys performed a temporal-order memory task (Naya & Suzuki, 2011). In the task, a sequence of two cue stimuli was shown for 0.3 sec each with a delay interval (0.9 sec) between them. After the encoding phase, the animal was required to touch the two items in the same order as they were presented. We recorded 127 neurons from the dorsolateral PFC. We examined stimulus-selectivity for each recorded neuron using one-way ANOVA and found that 19 PFC neurons exhibited stimulus-selective activities for the first cue (P < 0.05) and 15 neurons showed significant stimulus-selectivity for the second cue. The number of neurons with stimulus-selective responses for both cues (n = 2) did not differ (P = 0.89) from the chance (i.e., 19Χ15/127). In striking contrast to the PFC, we found significantly larger numbers of neurons showed stimulus selectivity for both cues in the perirhinal cortex (P < 0.001) and the entorhinal cortex (P < 0.001) of MTL as well as area TE (P < 0.005). The hippocampus was excluded from this analysis because it did not have substantial number of neurons with stimulus selectivity for each cue. These results indicate differential contributions of PFC and MTL to the encoding of temporal order memory.