Oxamyl, a carbamate insecticide, is mainly used to control nematodes in the agricultural field. Although oxamyl is a widely used insecticide that is associated with ecological concerns, limited studies have examined the toxic effects of oxamyl on the developmental stage and the underlying mechanisms. In this study, the developmental toxicity of oxamyl was demonstrated using zebrafish, which is a representative model as it is associated with rapid embryogenesis and a toxic response similar to that of other vertebrates. The morphological alteration of zebrafish larvae was analyzed to confirm the sub-lethal toxicity of oxamyl. Analysis of transgenic zebrafish (olig2:dsRED and flk1:eGFP line) and mRNA levels of genes associated with individual organ development revealed that oxamyl exerted toxic effects on the development of neuron, notochord, and vascular system. Next, the adverse effect of oxamyl on the mitochondrial electron transport chain was examined. Treatment with oxamyl altered the PI3K/Akt signaling and p38 Mapk signaling pathways in zebrafish. Thus, this study elucidated the mechanisms underlying the developmental toxicity of oxamyl and provided information on the parameters to assess the developmental toxicity of other environmental contaminants.