Herbal extracts are known for their antioxidant, antimicrobial, and anti-inflammatory properties. However, the intense colour caused by their phenolic content and dark-coloured compounds may spoil the final product’s appearance. To remedy that, this study was undertaken to design a decolourization device to eliminate the intense colour of herbal extracts while retaining their beneficial properties. Batch experiments have been conducted to study decolourization and its effect on extract quality. From there, a decolourization device has been devised using activated carbon. Operating at optimum conditions, the device was able reduce 81 % of the total phenolic content of cashew leaf extracts while retaining 88 % of its radical scavenging capacity. Furthermore, the device is able to re-design the extract’s colour to fulfill the end-user’s needs by manipulating the contact period. The design of this device best fits Langmuir isotherm which demonstrates monolayer coverage of adsorbate at the outer surface of activated carbon