Few anthropogenic radionuclides like Cs-137 are difficult to detect. It needs a method to evaluate the environment quality based on molecular network of an organism exposed to the radionuclide arises, and the said method is called Biomonitoring. In this study, biokinetic experiment is conducted with the determination of Concentration Factor (CF) and Bioaccumulation Factor values of Cs-137 in goldfish (Cyprinus carpio) by means of freshwater influenced by its aquatic environment condition, which is potassium ion concentration (K+). CF value of Cs-137 concentration in Cyprinus carpio after the end accumulation in media conditioned with variation of potassium concentration 2.5; 5; 7.5 and 10 ppm, respectively are 2.762; 2.645; 2.637; 2.568 mL.g−1 and Bioconcentration Factor (BCF) for variation of K+ ion concentration 2.5; 5; 7.5 and 10 ppm, respectively are 1.32; 2.12; 1.77; 2.07 ml.g−1. Based on those values, goldfish (Cyprinus carpio) cannot be categorized as bioindicator for Cs-137.