The studies of any possiblity that heavy metals such as copper (Cu), lead (Pb), cadmium (Cd), chromium (Cr), iron (Fe), zinc (Zn), manganese (Mn) and nickel (Ni) and other azo dyes such as Reactive Orange 16, Red 106 and Yellow 42 will interfere the measurement of RB5 using the differential pulse cathodic stripping voltammetry (DPCSV) technique are described. This study is a part of method development for voltammetric determination of RB5 which will be used to analyze wastewaters from batik industry. A 2 mg/L RB5 was firstly scanned under the optimum parameters, followed by addition of a series of concentration from 2 to 5 mg/L of each metals and other reactive azo dyes standard solutions into voltammetric cell containing 2 mg/L RB5. Results show that the present of 2 mg/L Fe, 3 mg/L Cu and more than 3 mg/L Ni, Mn, Pb, Cd, Zn and Cr have interfered the measurement of 2 mg/L RB5. All azo dyes at 2 mg/L level interfered the measurement of RB5.