Justicia gendarussa (Acanthaceae) or commonly known as Gendarussa has traditionally been used to treat bone fractures. Bone fracture is a clinical condition that need bone repair and new bone formation. To date, the mechanism of Justicia gendarussa acting in enhancing the bone mineralization has not been proven scientifically. The present study aimed to investigate the cytotoxicity and alkaline phosphatase (ALP) activity on osteoblast cells when treated with Justicia gendarussa ethanolic leaves extract. MTT and ALP assays were performed on osteoblast cells after being treated with different concentrations of theextract. For cell viability, the result showed that IC50 value of the osteoblast cells was 89.1μg/ml. While, ALP assay is used as a biochemical marker for early detection of osteoblast mineralization. The highest amount of ALP activity was at the 37.5 μg/ml when compared to the control. From this study, it shows that Justicia gendarussa has potential in enhancing bone mineralization during the bone repair process.