Geopolymer is a promising green building material compared to Portland cement. It is produced by activating the aluminosilicate materials rich in Si and Al with alkaline solution (sodium hydroxide and sodium silicate) (NaOH and Na2SiO3). As one of the largest palm oil producers globally, Malaysia generates significant amounts of waste, including palm oil fuel ash (POFA) and palm oil boiler ash (POBA), during the processing of palm oil. While POBA is rich in SiO2, it lacks sufficient Al2O3 to undergo geopolymerization, limiting its potential for geopolymer production. This experiment studies the effect of NaOH concentration (NaOH conc), solid-to-liquid mass ratio (S/L mass ratio), and percentage mass of alumina powder (Al2O3) replacement on the compressive strength of POBA-based geopolymer. The Na2SiO3/NaOH volume ratio and curing temperature were fixed at 2 and \(80\,^\circ {\text{C}}\) , respectively. During the experiment, a total of 12 designs were evaluated to optimize the parameters. The study ranges identified for NaOH concentrations, B/L mass ratio, and percentage mass of Al2O3 for POBA-based geopolymer were 5 M to 20 M, 1 to 2.5, and 5% to 30%, respectively. The experiment result indicates that the optimum mixing ratio for POBA-based geopolymer has NaOH concentration of 15 M, S/L mass ratio of 1.5, and 25% Al2O3 replacement, yielding the highest compressive strength at 7 days.