MFI-type(ZSM-5) zeolite nanocrystals with SiO2/Al2O3 ratios of 100 has been synthesized through crystallization of gel in mesoporous system of carbon nanotubes(CNTS) with internal diameter of 20~30nm. Investigation by using X-ray diffraction (XRD), Fourier transform infrared (FT-IR), transmission electron microscope (TEM) and scanning electron microscope (SEM) shows that the nanocrystals possess the typical nanosized zeolites structural characteristics which is different from those of microsized zeolites. Compared with those of the corresponding sample synthesized in hydrothermal system, the bands of the nanosized sample are shifted slightly to lower or higher wavenumbers. The TEM images of the purified carbon nanotubes and nanosized ZSM-5 crystals after the removal of the carbon matrix suggest that clean and homogeneous carbon nanotubes have internal diameters of approximately 20~30 nm and the most crystal sizes are in the range 30~60nm. The SEM photograph verifies the existing of nanosized ZSM-5.