Organisms and pathogens found in ballast water have had significant economic and ecological impact on marine biodiversity in many regions. An efficient way to address this issue is the physical and/or chemical treatment of ballast water on board. For the majority of ballast water treatment systems using oxidative compounds, the formation of chemical by-products (CBPs) is an issue, and could cause adverse effects on aquatic organisms. In this paper, treated ballast water is analyzed for CBPs that might be produced after treatment based on an advanced oxidation process. Effects of storage time of treated samples (i.e., after treatment), active substances dosages, pH and temperature on the formation of CBPs, including trihalomethanes (THMs), haloacetic acids (HAAs), haloacetonitriles (HANs), haloketones (HKs), trichloronitromethane (TCNM) and chloral hydrate (CH) were investigated. No HKs and CH were found under all conditions. THMs followed an increasing then decreasing pattern with prolonged storage time of treated samples, but HAAs declined over time. Linear relationships were observed between the formation of CBPs and active substances dosages. Different pH values in the range from 4 to 9 caused a different shift in the formation of the measured CBPs. An increase in temperature enhanced the formation of THMs and HAAs, but decreased the formation of HANs and did not affect TCNM formation significantly. Compared with algal cells, the contribution of humic acid (HA) to the formation of CBPs was investigated. Algal cells exhibited the largest impact on nitrogenous CBPs formation, however, HA played a greater role in carbonaceous CBPs formation. (C) 2013 Elsevier B.V. All rights reserved.