The present study was designed to determine the changes of phosphorylation of cAMP- response element binding protein (CREB) in hippocampus induced by ohmefentanyl stereoisomers (F9202 and F9204) in conditioned place preference (CPP) paradigm. The results showed that mice receiving F9202 and F9204 displayed obvious CPP. They could all significantly stimulate CREB phosphorylation and maintained for a long time without affecting total CREB protein levels. The effect of F9204 was similar to morphine which effect was more potent and longer than F9202. We also examined the effects of ketamine, a noncompetitive N-mthyl-D-aspartate receptor (NR) antagonist, on morphine-, F9202- and F9204- induced CPP and phosphorylation of CREB in hippocampus. Ketamine could suppress not only the place preference but also the phosphorylation of CREB produced by morphine, F9202 and F9204. These findings suggest that alterations in the phosphorylation of CREB be relevant to opiates signaling and the development of opiates dependence. NR antagonists may interfere with opiates dependence and may have potential therapeutic implications.