A KOH/ZrO2 catalyst was used as a solid base catalyst for biodiesel production via transesterification of palm oil with methanol using a batch reactor. The catalytic activity of KOH/ZrO2 is associated with the active phase (K2O) and basic properties. The catalysts were characterized by using BET, XRD, SEM, CO2-TPD, and Hammett indicators.The highest methyl ester content of 99% was obtained when the highest basic strength (15