This study aims to evaluate the performance of ozone treatment for removing N-nitrosamines from reverse osmosis (RO) concentrate in water recycling applications. In the absence of any N-nitrosamine precursors, the destruction efficiency of N-nitrosamines was dependent on their molecular weight or the length of the alkyl chain in their molecular structure. Experiments conducted with RO concentrate showed that ozonation could lead to the formation of N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine (NDEA), resulting in an increase in concentrations of these N-nitrosamines. Nevertheless, ozonation was effective for destruction of N-nitrosamines with molecular weight greater than that of NDEA (102 g/mol). © 2014 Copyright © 2014 International Ozone Association.