PP-R/OMMT and PP-R/OMMT/PP-MA nanocomposites were synthesized by melting intercalation. Small angle X-ray method was used to investigate the changes of interlayer distance of OMMT in the nanocomposites. The thermal properties were tested via DSC and TGA. Microstructure of the nanocomposites was detected by TEM. The results show that with increasing amount of OMMT, linear thermal expansion coefficient of PP-R/OMMT nanocomposites decreases and thermal decomposition temperature rises. With increasing amount of PP-MA, thermal decomposition temperature of PP-R/OMMT/PP-MA nanocomposites rises initially and decreases afterwards.