© 2016 The Authors. Objective: To determine optimal conditions required for activated charcoal production from rice straw with high quality for medical and pharmaceutical applications using chemical activation process. Methods: Effects of different pretreatment protocols in 2-step H 3 PO 4 activation of Thai rice straw on adsorption properties, pore structure, and surface chemistry were investigated. The rice straw was carbonized at 400 °C for 2 h. The obtained charcoal was then impregnated with 85% H 3 PO 4 in the ratio of 1:4 w/v for 24 h, followed by carbonization at 500, 600 and 700 °C for 1 h. Results: The results indicated that the 2-step H 3 PO 4 activation, impregnating and carbonization at 700 °C was more efficient in producing activated charcoal because of showing the highest iodine adsorption (629 mg/g), methylene blue adsorption (198 mg/g) and Pb 2+ ions adsorption (64.19%). The adsorption capacity on iodine, methylene blue, and Pb 2+ ions were compared. The results showed that rice straw activated charcoal was most efficient highest to adsorb Pb 2+ ions. This adsorption capacity was higher than that of the commercial medical-grade activated charcoal. Conclusion: The rice straw activated charcoal which was prepared by 2-step H 3 PO 4 .