Crop improvement represents the genetic alteration of plants to gratify human needs. Crop improvement, the art of engineering plants for the benefit of humankind, is as old as agriculture itself. Even though crop improvement programs focus on the development of novel crop varieties with enhanced quality and tolerance to ecological stresses (both biotic and abiotic) and making crops able to give more yield exhibiting good quality. Still, we cannot rely on the crops due to various reasons, like the irritating nature of onion, low lysine and threonine content in Maize, the presence of toxic Gossypol in cotton, etc. These irritating qualities of the crop must be reduced or removed by genetically modifying the crop plants, and then only it will be accepted for human consumption. Expression of antisense genes and the related genesilencing technique has been exploited as an applied technique in plant biotechnology for creating “metabolic engineered plants” in which the endogenous target gene, which is responsible for the unpleasant character is specifically suppressed. The antisense and its related technology are used for various purposes such as silencing or ablating undesired genes. In the present chapter, the down-regulation of the enzyme using the gene-silencing technique used in various crop varieties are discussed in detail.