The study aimed to evaluate the treatment efficiency of Methylene Blue in wastewater by bio-activated carbon material which prepared from Macadamia nutshells using H₃PO₄ activating agent at the ratio of 2 H₃PO₄ : 1 activated carbon. The bio-activated carbon material was prepared and used to survey its effected parameters included treatment temperature and time at lab-scale. The research result showed that at respectively optimal temperature and time of 500^oC and 60 minutes, 1 g of bio-activated carbon will absorb 116.91 mg of Methylene Blue. The result shows that the colour treating efficiency of Methylene Blue is 97.11% corresponding to the colour level reduced from 349.67 Pt-Co to 10.11 Pt-Co. The bio-activated carbon prepared from Macadamia nutshell using H₃PO₄ activating agent could treat colour in dyeing textile wastewater.