In this study, Cu (II) was determined with a carbon paste electrode modified with Mesorhizobium opportonistum bacteria species used for the first time in the production of a microbial biosensor (MOMB). Cu (II) ions were first accumulated on an electrode surface via open circuit, then electrochemical determination was conducted with cyclic and differential pulse cathodic stripping voltammetry techniques. Experimental conditions such as pH, scan rate etc. were optimized. The MOMB exhibited linearity in the range of 5.0x10(-8) M to 2.0x10(-6) M for Cu (II) (correlation coefficients: 0.9914) with detection limit (LOD) of 2.0x10(-8) M, a limit of quantification (LOQ) 6.64x10(-8) M and a detection sensitivity (10.34 mu A/mu M), for Cu (II). The electrode-to electrode reproducibility of the MOMB was found to be 2.41 % (n=6) coefficient of variation. The MOMB has advantages for Cu (II) determination, including good sensitivity and reproducibility, easy preparation, low cost, applicability to sample and not having a need for additional chemical processes.