By utilizing carboxylated multiwalled carbon nanotubes (MWCNT-COOH) to strengthen the interaction between the electrode and the analytes and improve the conductivity of the composite material and in conjunction with the superior catalytic properties of copper-based metal-organic framework (MOFs), a novel electrochemical sensor was fabricated from a Cu-MOF/MWCNT-COOH composite, specifically designed for the simultaneous and distinct detection of ascorbic acid (AA) and dopamine (DA). Electrochemical analyses were conducted on the innovative Cu-MOF/MWCNT-COOH electrode through both CV and DPV, revealing unique electrochemical behaviors for AA and DA. The sensor not only showed exceptional electrocatalytic properties but also distinguished itself by its broad dynamic response ranges, covering concentrations from 3 to 1800 μM for AA and from 2 to 180 μM for DA, with detection limits (S/N = 3) of 3.00 μM for AA and 0.32 μM for DA. Furthermore, this electrochemical detection platform exhibited robust reproducibility and selectivity. Examinations of serum samples yielded the recovery rates of AA and DA which were 101.9% and 102.1%, respectively, confirming the sensor's capability to perform reliably under varied biological conditions. The findings confirm the sensor's potential of the proposed method for the simultaneous, sensitive, and reliable detection of AA and DA. In conclusion, the electrochemical sensor has a promising potential for practical applications.