A various organic modifiers depending on the substituents of ammonium ions were synthesized and used to prepare organically modified montmorillonite (OMMT). Nitrile-butadiene rubber (NBR)/OMMT nanocomposites could be obtained using melt-compounding followed by hot-press vulcanization. d-Spacings of OMMT were changed as the chemical structures of modifiers were varied. X-ray diffraction (XRD) and tensile measurements of NBR nanocomposites revealed that the structures of organic modifiers affect the properties of NBR nanocomposites after vulcanization. Long alkyl chain of OMMT induced higher interaction between NBR and OMMT, resulting in higher tensile strength, Young’s modulus, and hardness of NBR/OMMT nanocomposites.