This study was performed to develop software sensorsto predict the BOD5 of river water and wastewater. The software sensors were based on the multiple-regression analysis using the dissolved organic carbon(DOC) concentration, UV light absorbance at 254nm and synchronous fluorescence spectra. River water samples and wastewater treatment plant (WWTP)effluents were collected at 1-hour interval to evaluatethe feasibility of the software sensors.