Cesium generated from nuclear power plants is the primary source of problems for human health and environment due to its gamma radiation and high fission yield. Among the cesium removal methods, adsorption is an effective way to separating it from water. The abundance, retrievability, and selectivity of an adsorbent are crucial for its practical application in wide areas. Herein, we report a simple and environment-friendly synthesis of montmorillonite-prussian blue (MMT-PB) hybrid adsorbents and studies of the kinetic and equilibrium adsorption. Even though chemisorption (ion exchange) was dominant, physisorption (ion trapping) also occurred especially for the MMT-PB hybrid. The maximum adsorption capacity of MMT-PB was 57.47 mg/g, which was high enough as compared favorably with that of previously reported adsorbents. The distribution coefficient (K-d) of the hybrid was examined in the presence of prevalent cations such as Na+, K+, Ca2+, and Mg2+ to analyze its selectivity. The K-d value ranged from 3680 to 13700 mL/g at a cation concentration of 0.001 M. Moreover, the divalent cations prevented cesium adsorption due to its high electrostatic interactions with the adsorbent. The K-d decreased, ranging from 973 to 4160 mL/g, at a cation concentration of 0.1 M. In this case, K+ significantly prevented cesium adsorption as their hydrated radii are similar. Considering the low concentration of K+ in nature, the MMT-PB hybrid shows great promise for large-scale application in cesium removal from soil and contaminated water.