PMMA/Na-MMT nanocomposites were synthesized through a soap-free emulsion polymerization of methyl methacrylate (MMA) using 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). A conventional anionic surfactant, dodecylbenzenesulfonic acid sodium salt (DBS-Na), was also used to compare with AMPS in the interaction with pristine Na-MMT. Both surfactants were intercalated into the layers of the pristine Na-MMT dispersed in water before polymerization. The nanocomposites with AMPS were exfoliated during polymerization because AMPS made the polymer end-tethered on pristine Na-MMT. The nanocomposites were exfoliated up to the 10 wt% content of pristine Na-MMT relative to the amount of MMA. The molecular weight of PMMA obtained from the nanocomposite with AMPS decreased, and the glass transition temperature (T-g) and storage modulus (E') of the nanocomposites became higher as the amount of Na-MMT increased.