Scale formation is a serious problem in many industries, especially in oil and gas industries. Therefore, in order to control the problems, this research studied the effect of the addition of gambier extract modified with kemenyan extract on the growth of calcium sulfate (CaSO4) scale formation as a green inhibitor. The crystallization experiments were carried out by using unseeded experiment method at temperature of 90°C. The CaSO4 crystals obtained with and without the addition of inhibitor were analyzed by scanning electron microscopy (SEM), particle size analyzer (PSA), and X-ray diffraction (XRD). The results of this experiment show that the addition of the combination of gambier and kemenyan extract with ratio of 5:9 can inhibit the growth of CaSO4 crystals with the inhibition effectivity of 39.88%. These results were supported from the SEM and PSA data showing that the crystal size and particle size distribution of the CaSO4 in the addition of the inhibitor are smaller than without the addition of inhibitor. In addition, analysis using XRD showed that CaSO4 crystals undergo a change in crystalline phase with the addition of inhibitors.