Cement replacement materials have been widely used to reduce adverse environmental impacts, increase the strength and durability of concrete, such as fume silica, slag, fly ash or natural pozzolan (volcanic ash). Volcanic ash is material that released from the earth when volcanic eruptions occur. Volcanic ash becomes an important environmental issue because it disturbs the balance of the environment. Volcanic ash is a very fine pyroclastic material, has a characteristic form of diversity. In the field of engineering, the usage of volcanic ash as added ingredients is still very limited, while active volcanoes emit volcanic ash every year. The purpose of this study is to determine the effect of added materials-volcanic ash of Dukono mountain to the mortar mixture. In this research, the test of compressive strength and mortar absorption. This research uses added material-volcanic ash from Dukono mountain. Preparation of test specimens with FAS value 0.4 with volcanic ash composition 0%, 5%, 10%, 15%, 20% and 25% to the weight of cement. The results of the compressive strength test average mortar with the composition of volcanic ash as added ingredients, increased compressive strength with the addition of volcanic ash