Display omitted •Spherical carbon was obtained from hydrothermal treatment (HT) of sucrose.•HT in conjunction with subsequent KOH activation produced activated carbon (AC).•AC has a BET surface area of 1534m2g−1 and 82.6% of micropores.•The Methylene Blue maximum monolayer adsorption capacity on AC was 704.2mgg−1. This work reports the synthesis of activated carbon (AC) obtained by KOH chemical activation of spherical carbon (SC) produced from hydrothermal treatment (HT) of sucrose. Scanning electron microscopy was used to characterize the morphology and the sphere sizes of SC, which showed average diameter of 2.86μm. SC showed low values of BET surface area (SBET) and total volume of pores (VT), whereas AC presented characteristics of microporous materials with SBET and VT of 1534m2g−1 and 0.765cm3g−1, respectively. FT-IR analysis and Boehm method indicated that the AC surface has essentially acid functional groups, which was confirmed by pHPZC values of 3.0. The adsorption equilibrium data of Methylene Blue (MB) onto AC were best fitted to the Redlich–Peterson model. The maximum adsorption capacity monolayer was of 704.2mgg−1, which showed to be high compared to other ACs reported in the literature. The kinetic data showed better fit to the pseudo-first-order model at low MB concentration, and with the increasing of concentration, to the pseudo-second-order and Elovich models. Thermodynamic parameters indicated that MB–AC adsorption process is spontaneous and endothermic.