We present the latest results from the Mission Program NIRLT, the NIR spectroscopic observations of brown dwarfs using the IRC on board AKARI. The near-infrared spectra in the wavelength range between 2.5 and $5.0{mu}m$ is especially important to study the brown dwarf atmospheres because of the presence of non-blended bands of major molecules, including $CH_4$ at $3.3{mu}m$, $CO_2$ at $4.2{mu}m$, CO at $4.6{mu}m$ and $H_2O$ around $2.7{mu}m$. Our observations were carried out in the grism-mode resulting in a spectral resolution of ~ 120. In total, 27 sources were observed and 18 good spectra were obtained. We investigate the behavior of three molecular absorption bands, CO, $CH_4$ and $CO_2$, in brown dwarf spectra relative to their spectral types. We find that the $CH_4$ band appears in the spectra of dwarfs later than L5 and CO band is seen in the spectra of all spectral types. $CO_2$ is detected in the spectra of late-L and T type dwarfs.