Two-dimensional melting and phase changes of binary mixtures of CCl 4 and CHCl3 confined in activated carbon fiber were examined using differential thermal analysis and 1H wide-line NMR. Molecular assembly of CCl4 confined in ACF nanospace with a slit width of 1.1 nm showed succeeding thermal anomalies corresponding to crystalhexatic and hexaticliquid transitions. Results showed that these thermal anomalies did not occur in a mixture of CHCl3 and CCl4. This behavior differed greatly from the phase diagram for the bulk mixture between CHCl 3 and CCl4. Furthermore, the dynamic features of CHCl 3 molecule were examined using the 1H wide-line NMR spectrum. The activation energy of the hopping motion changed from 7 kJmol-1 for pure CHCl3 to 13 kJmol-1 for CHCl3 with a 0.016 molar ratio in CCl4. In particular, a drastic increase in the activation energy was observed for doping with a trace amount of CHCl 3, suggesting that molecular self-assembly of CCl4 takes place in the ACF nanoslit because of the effective intermolecular interaction between CCl4 molecules. The existence of CHCl3 in CCl 4 brings about the remarkable impurity effect on twodimensional melting and phase transition of CCl4 confined in ACF nanospace. © 2010 The Chemical Society of Japan.