Ballast water has been largely responsible for the global transfer of harmful aquatic organisms. When discharged into a new environment, some aquatic plants and animals carried in ballast water may become invaders and seriously disrupt the native ecology and economy. Moreover, human pathogenic microorganisms carried in ballast water have threatened human health. The extent of the transfer of harmful aquatic organisms via ballast water has increased with growing maritime activity and larger and faster vessels. Unlike other forms of marine pollution, the impacts of invasive marine species are most often irreversible. As a result, marine ecosystems are being changed. This paper will illustrate how the serious environmental problem arises due to the uncontrolled discharge of ballast water.