The synthetic flame retardant tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) has been frequently detected in natural waters, and its maximum concentration ever reported is 377 ng/L. However, information on the adverse effects of environmentally relevant concentrations of TDCIPP on aquatic organisms are totally unknown. In this study, <12-h old water fleas, D. magna, were exposed to concentrations of 0, 65±7.1, 550±33, or 6500±1400 ng/L TDCIPP, and dose- and time-dependent effects on reproduction and development were evaluated. Sequences of genes of D. magna were obtained from the National Center for Biotechnology Information and were used to develop PCR arrays for D. magna. Arrays were then used to study transcriptional responses of D. magna to TDCIPP. Exposure to environmentally relevant concentrations of TDCIPP significantly decreased fecundity as well as length of F0 and F1 generations. Transcriptional responses showed that, of the 155 genes tested, expressions of 57 genes were significantly changed, and some changes occurred following exposure to environmentally relevant concentrations (i.e., 65±7.1 and 550±23 ng/L). Furthermore, pathways related to protein synthesis and metabolism and endocytosis were considered to be significantly affected in a dose- and time-dependent manner and might be responsible for TDCIPP-induced reproductive and developmental toxicities.