In this work a sensitive electrochemical sensor for simultaneous determination of morphine and codeine constructed by application of disposable screen printed carbon electrode strips (SPCE) modified by double strand (ds) calf thymus DNA. According to the results of the modified SPCE strips and experimented parameters, we observed a considerable shift between potentials of morphine and codeine current peaks. Related to these observed shifts, we studied on the effect of the concentration of modifier and pH value on the anodic oxidation pattern of morphine and codeine in the case of optimize the method to get better signals with maximum potential distance. Also to boosting the LODs of this electroanalytical method coupled with an electro-membrane preconcentration (EME) step. The calibration curve which was plotted by the variation of differential pulse voltammetry (DPV) currents as a function of different morphine and codeine concentration were linear within the range of 0.7– 40 μM and 2.3- 40 μM for morphine and codeine respectively. Also the limits of detection were 0.07 μM and 0.23 μM, respectively. Finally, the proposed method was able to determine morphine and codeine simultaneously and effectively in urinary real samples.