Despite the well known benefits of omega 3 (n-3) polyunsaturated fatty acids (PUFA) supplementation on human health, relatively little is known about the effect of n-3 PUFA intake on fertility. More specifically, the aim of this study was to determine how oocyte and pre-implantation embryo development may be influenced by n-3 PUFA supply, and to understand the possible mechanisms underlying these effects. Adult female mice were fed a control diet or a diet relatively high in the long-chained n-3 PUFAs for 4 weeks, and ovulated oocytes or zygotes were collected after gonadotrophin stimulation. Oocytes were examined for mitochondrial parameters (active mitochondrial distribution, mitochondrial calcium and membrane potential) and oxidative stress, and embryo developmental ability was assessed the blastocyst stage following a) in vitro fertilization (IVF) or b) culture of in vivo derived zygotes. This study demonstrated that exposure of the oocyte during maturation in the ovary to a high n-3 PUFA environment resulted in altered mitochondrial distribution and calcium levels, and increased production of reactive oxygen species. Despite normal fertilization and development in vitro following IVF, the exposure of oocytes to a high n-3 PUFA environment during in vivo fertilization adversely affected the morphological appearance of the embryo and decreased developmental ability to the blastocyst stage. This study suggests that high maternal dietary n-3 PUFA exposure peri-conception reduces normal embryo development in the mouse and is associated with perturbed mitochondrial metabolism, raising questions regarding supplementation with n-3 PUFAs during this period of time.