Nanoparticle (NP) exposure may induce oxidative stress through generation of reactive oxygen and nitrogen species, which can lead to cellular and tissue damage. The digestive system is one of the initial organs affected by NP exposure. Here, it is demonstrated that exposure to metal oxide NPs induces differential changes in zebrafish intestinal NO concentrations. Intestinal NO concentrations are quantified electrochemically with a carbon fiber microelectrode inserted in the intestine of live embryos. Specificity of the electrochemical signals is demonstrated by NO-specific pharmacological manipulations and the results are correlated with the 4,5-diaminofluorescein-diacetate (DAF-FM-DA). NPs are demonstrated to either induce or reduce physiological NO levels depending on their redox reactivity, type and dose. NO level is altered following exposure of zebrafish embryos to CuO and CeO2 NPs at various stages and concentrations. CuO NPs increase NO concentration, suggesting an intestinal oxidative damage. In contrast, low CeO2 NP concentration exposure significantly reduces NO levels, suggesting NO scavenging activity. However, high concentration exposure results in increased NO. Alterations in NO concentration suggest changes in intestinal physiology and oxidative stress, which will ultimately correspond to NPs toxicity. This work also demonstrates the use of electrochemistry to monitor in vivo changes of NO within zebrafish organs.