A metakaolin-based geopolymer microsphere (GM) was prepared from metakaolin and modified water glass by a dispersion suspension and solidification method. The morphology of the GM was characterized by SEM, XRD, FTIR and BET studies. Its adsorption performance and mechanism of GM towords Methylene blue (MB) were studied. The results showed that the adsorption process of MB onto GM could be described by the pseudo-first-order model and Langmuir adsorption isotherm model. The maximum theoretical adsorption capacity of MB onto GM was 100.1 mg/g. The adsorption process of MB by GM was a spontaneous and endothermic process. Furthermore, after using GM for 5 cycles, the removal rate of MB by GM can still reach 81.56%, which is easy to recycle and regenerate. GM had strong selective adsorption ability to cationic dyes, by comparing adsorption ability of cationic and anionic dyes. The GM was low-cost, efficient, green and sustainable adsorbents for removal of cationic dyes in water.