With cationic and anionic surfactants cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfonate (SDS) as modifiers, Ca-montmorillonites (Ca-Mt), artificial Na-montmorillonites (R-Na-Mt) and natural Na-montmorillonites (Na-Mt) with different cation exchange capacity (CEC) were modified by solution intercalation method, respectively. Then cation-anion organo-montmorillonites (OMt) were prepared. The influence of CEC on the basal spacing of cation-anion OMt and the influence mechanism were discussed by X-ray diffraction (XRD) and zeta potential testing. The results indicate that the basal spacing of cation-anion OMt is related to CEC. For the same type montmorillonites, the basal spacing of cation-anion OMt decreases with the increase of CEC and it is easier to get cation-anion OMt with greater basal spacing when CEC is lower. Moreover, the CEC of Na-Mt has the greatest influence on the basal spacing of cation-anion OMt. (C) 2014 Elsevier Ltd. All rights reserved.