Co-transport behavior of carboxylated multiwalled carbon nanotubes (COOH-MWCNTs) and kaolinite in various solution ionic strength (IS) and pH were investigated. Results on electrophoretic mobility of CNT, kaolinite and quartz sand as well as particle size of CNT-kaolinite mixture, CNT alone and kaolinite alone were consistent with the DLVO theory. Large particle sizes of kaolinite-CNT mixture revealed potential heteroaggregations especially at 1 mM NaCl, pH=3 and 10 mM NaCl and pH=9. Deposition of CNT was enhanced during the co-transport at 1mM NaCl and pH=3 due to the low mobility of CNT-kaolinite heteroaggregate while decreased at pH=5 in 1 mM NaCl, pH=9 in 10 mM NaCl and pH=9 in 100 mM NaCl because of site blocking by kaolinite. Kaolinite mobility increased in the presence of CNT at pH=3 in 1 mM NaCl caused by site blocking and at pH=9 in 10 mM NaCl resulted from low single collector efficiency of large particles.