Differential scanning calorimetry (DSC) and time-resolved X-ray diffraction (XRD) were used to elucidate the mechanism of isothermal palm oil crystallization at 25 degrees C and gain more insight into the effect of monoglycerides (MGs) on the palm oil crystallization behavior. At this temperature, it was confirmed that palm oil first partially crystallizes from the melt in cc crystals before beta' crystals are formed by a polymorphic transition. Subsequently, additional beta' crystals are formed directly from the melt. MGs Of Sunflower oil (MGSFO) only accelerate the polymorphic transition whereas MGs of hydrogenated palm oil (MGHPO) additionally promote the nucleation of the a crystals. The homogeneity between the fatty acids of MGHPO of palm oil and the higher degree of saturation of MGHPO are Suggested as the main causes for the larger effectiveness in accelerating palm oil crystallization.