A precise and simple in-situ voltammetric measurement of promethazine, based on the nano sized molecularly imprinted polymer (nano-MIP) was introduced. The nano-MIP was synthesized utilizing vinyl benzene and Divinylbenzene as the functional monomer and cross-linker respectively, and via the micro-emulsion polymerization method in silicon oil. The MIP particles were then embedded in a carbon paste electrode (CPE) in order to prepare the MIP-CP electrode. This electrode showed higher response to analyte, compared to the both bare CPE and modified with non-imprinted polymer. Also, the selectivity of the MIP-CPE was investigated using some of the cross reactants and the sensor was clearly selective towards the PMZ. Various factors, known to affect the response behavior of the sensor, were investigated and optimized. This sensor exhibited two distinct linear response ranges of 4× 10-9-4×10-7 M and 4×10- -7×10-6 M in optimum analysis conditions. Limit of detection was calculated equal to 1.4×10-9 M (S/N). An interestingly low RSD equal to 1.2% was found for 4 separate determinations by the proposed sensor. The sensor was applied for PMZ in-situ determination in plasma samples without applying any sample pretreatment.