High alkali and alkaline earth metals (AAEMs) present in oil palm empty fruit bunch (EFB) can cause the secondary reaction during the pyrolysis and this problem leads to the low bio-oil yield with high formation of char. In this study, a new effective technique to eliminate the AAEMs from EFB was revealed by sonication using ultrasonic bath in the presence of nitric acid. The operating variables such as different AAEMs removal techniques, leaching solutions and leaching time were investigated. The results indicated that the demineralization process was an effective pre-treatment due to the reduction of moisture and ash contents from 6.5 % to 2.3 % and 4.5 % to 0.95 %, respectively in the treated EFB. In addition, about 82.42 % of ash was eliminated from EFB using 1 % of nitric acid at 10 minutes of sonicating time. Demineralization efficiency of AAEMs was monitored using Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES). The results showed that leaching with nitric acid eliminated all alkali metals (K and Na) from EFB, while, alkaline earth metals (Mg, Ca and Fe) had different degree of demineralization efficiency in comparison to water soaking technique. Therefore, these findings showed that sonication with nitric acid was an effective leaching technique with comparison to water soaking. This work discloses a favourable demineralization process as biomass pre-treatment for bio-oil upgrading with shorter time ash removal from EFB.