Indonesia is a country that produces the largest coconut in the world. 35% of the coconut volume is coir. Coir is a waste that has not been widely used for construction work. The coir fibers have the highest tensile strength among other natural fibers and have resistance to compressive forces. In this study, the unconfined compressive strength (UCS) of clay strengthened with coconut fiber is presented. The specimens were made with the fiber percentage of 0.00%; 0.25%; 0.50%; 0.75%; and 1.00% by weight of the mixture. This study concluded that the clay's UCS has increased along with the more coconut fiber added. The maximum value of UCS and secant modulus was obtained in clay with fibers of 0.75%. The clay strengthened with coconut fiber becomes stiffer than the initial clay, thereby improving its soil stability.