Oil pollution from food industries is one of the major environmental concerns nowadays. Improper management and disposal of cooking oils into the drainage system can have undesirable effects on the environment. However, one of the best ways to treat oil pollution is adsorption using activated carbon. In this study, rubber seed kernels (RSKs) were used to produce activated carbon via impregnation with 10 and 15 wt.% phosphoric acid (H3PO4). Then, the chemically impregnated RSKs were carbonised at 300, 400, and 500 °C for 1.5 h. The performance of the synthesised rubber seed kernel activated carbon (RSKAC) was evaluated based on its oil adsorption capacity. Samples of raw RSKs and RSKAC were analysed using Scanning Electron Microscopy (SEM) and Fourier-transform Infrared (FTIR) spectroscopy. The results showed that RSK sample impregnated with 10 wt.% H3PO4 and carbonised at 500 °C has the highest oil adsorption capacity of 0.896 ± 0.042 g/g. The SEM results showed that the RSKAC sample has more pores than the RSK sample. FTIR spectra of RSKAC revealed that peaks associated with four functional groups (O-H, C-H, C-O, and C=O) were reduced, or disappeared after undergoing H3PO4 activation. These findings revealed that RSKAC has the potential to be utilised as an adsorbent for oil adsorption.