The use of mortar in construction is widely attributed to its strength and durability. It is traditionally achieved through a mixture of cement, water, and fine aggregates. Increasing environmental concerns, however, have spurred research into improving the properties of mortar while reducing its ecological impact. Riau Province, with its vast oil palm plantations, produces a large amount of oil palm waste, which causes environmental pollution. At the same time, cement production as the main binder in mortar is a major contributor to air pollution and CO2 emissions. This research addresses this problem by exploring the potential of palm oil waste as an additive to replace cement in the production of lightweight mortar. The study investigated the mechanical properties of the mortar, specifically compressive strength, modulus of elasticity and as a novelty of the study added microstructure testing. Palm oil waste was incorporated in varying proportions of 2.5%, 7.5%, 12.5%, and 17.5% by weight of cement, and the samples were molded on 10 cm cubes. The results of the research for compressive strength testing, showed that the test specimens at the age of 28 days with a variation of 12.5% palm oil waste, produced an optimal compressive strength of 1.32 MPa. There was an increase of 55% compared to the specimens with 0% variation. This research represents the feasibility of reusing palm oil waste to improve mortar performance while addressing the environmental challenges posed by the industry. The resulting modulus of elasticity was 1,402 MPa. SEM test results showed that the mortar structure did not have large voids. XRF testing resulted in the palm oil waste mixture including class F and class C classifications in accordance with the requirements of ASTM C 618 in 2019. XRD results show at position [°2 theta] 26.705° with an enumeration value of 5.470.