Abstract: Ohmefentanyl is not only a potent analgesic agent, but also a selective ligand for μ opioid receptor, tn order to search for more(?)potent analgesics, more selective lingands and long duration of analgesic action in 3-methylfentanyl derivatives, we made modifications of the 1-phehethyl and 4-N-propionyl groups in 3-methylfentanyl and synthesized 15 new compounds. The analgesic activity, duration of analgesic action, receptor binding affinity and opioid sub-receptor selectivity of some of these compounds were measured. Primary pharmacological results showed that most of the compounds in this series possessed morphine-like effects. Thee analgesic activities of them were about 2～180 times more potent than that of morphine. The duration of analgesic action of the tested compounds was 6～10 times longer than that of fentanyl. The receptor binding affinities (IC₅₀) of compounds 1～4 were. 10^-7～10^-8 mol. Compound 13 displayed the best binding selectivity on μ opioid receptor site with ratio μ/δ>700 in rat brain membrane and μ/δ=1000 in mouse brain membrane. The new compound may be proposed as a useful tool in studying the opioid receptor. According to the result Of equations in reference 11, compounds 7～14 were designed and prepared. The observed logl/c values of them were much Closer to the calculated values.