Highly mesoporous activated carbons (ACs) with a mesopore fraction ranging from 42 to 73% were obtained by activation of rice straw (RS) with ortho-phosphoric acid (PA). Due to such a high mesoporosity, these ACs can be successfully used for pollutant removal in aqueous phase. The ACs were prepared at activation temperatures (T) ranging from 350 to 500 degrees C, using PA to RS weight ratios (R) from 0 to 1.6 and activation times from 0 to 2 h. They were characterised by nitrogen adsorption at -196 degrees C, SEM-EDX, and methylene blue adsorption. RS is a very heterogeneous material with a variable content of mineral matter: using the product of activated carbon yield multiplied by surface area (C x S-BET) as the performance criterion, the best AC was produced at T = 450 degrees C and R >= 1. These conditions lead to S-BET higher than 500 m(2) g(-1) and a C x S-BET around 270 m(2) g(-1). (C) 2010 Elsevier B.V. All rights reserved.