Chemical grouts were developed in response to a need to develop strength and control water flow in geologic units where the pore sizes in the rock or soil units were too small to allow the introduction of conventional Portland cement suspensions. Important advantages of chemical grouts are very high penetration power, less pumping pressure required for the same rate of grout injection, controllable setting time, severalty of commercial chemical grouts with different quality characteristics and quick action of grout in seepage control. Seepage control system of Karkheh dam is cutoff wall that is executed in all over the dam axis using plastic concrete. In part of conglomerate foundation of Karkheh dam, in region named gallery 950, is considered to create a water seal curtain due to impossibility of cutoff wall development. Because of the choice of cement grout curtain was not completely successful, therefore a water seal curtain using chemical grouts for first time in the country was designed by Mahab Ghodss consulting engineers to remove the problems arised from seepage in this part of dam foundation. Chemical grout testing in Karkheh dam proved the efficiency of the method in seepage control as well as resulted in valuable and unique experiences, among them are design of correct program for chemical grouting, mix design, solving execution problems and selection of proper preparation and grouting system. In this paper chemical grouting is briefly introduced then results and experiences obtained from chemical grout testing in Karkheh dam is presented.