Renewable diesel from hydrogenated palm olein can substitute fossil diesel. This study used an activated carbon pellets catalyst in a 500-ml autoclave to decarboxylate palm olein hydrothermally. The experiment was conducted at 330-400 °C, the catalyst-feed ratio was 0.7, and the water-palm olein (palm cooking oil) weight ratio was 4 to 1. GC-MS and standard alkane and alkene characterized liquid products, while GC-TCD identified gas products. Renewable diesel's highest yields are 13.24% and 3.15% for samples with and without activated carbon pellets catalysts at 370 °C. In conclusion, activated carbon pellets increase renewable diesel recovery in hydrothermal decarboxylation.