Nitrate is used in food processing, to enhance colour and to impart anti-microbial activity for the preservation of meat and meat products. However, nitrate can also be a contaminant that impacts on both environmental and human health. As a consequence, methods for accurate, fast and sensitive determination of nitrate are very important. Some spectrophotometric, chromatographic and electrochemical methods have been developed for nitrate determination. However, the requirements for low cost, a short time of analysis, sensitivity, simplicity, selectivity, stability and reliability can still not be met by a single analytical method, except by using biosensors. The main advantages offered by biosensors over conventional analytical techniques are the possibility of portability, miniaturization and working on-site, and the ability to measure pollutants in complex matrices with minimal sample preparation. Despite these advantages, the application of biosensors to the environmental field is still limited in comparison to medical or pharmaceutical applications. There are only a limited number of biosensoric studies on the determination of nitrate and nearly all of them are based on the enzyme nitrate reductase. However, in terms of applicability, nitrate reductase is fraught with practical issues when applied to biosensor assays. This is because nitrate reductase is not very active and there are problems associated with the direct transfer of electrons within the electrode systems used in such biosensors. Thus, microbial biosensors and inhibition type biosensors have been developed to address this. In this chapter, we focus on amperometric nitrate biosensors that have been applied to environmental health.