A grand canonical Monte Carlo simulation (GCMC) method is used to study adsorption in a carbon slit pore of finite length. Methane is used as a model for the nonpolar molecule, while the polar molecule is modeled as water. The behavior of a nonpolar molecule in the finite-length pore is investigated and compared with that obtained for a commonly used infinite slit pore. The adsorption of methane in the finite pore is significantly different from that in the infinite pore, both the capacity and the hysteresis loop. In addition to nonpolar molecules, the adsorption of water in finite pores has also been studied. The adsorption of water on activated carbon is very complex, and it strongly depends on the concentration as well as the position of the functional groups in the pore. For both cases of nonpolar and polar fluids, effects of pore size on the behavior of adsorption isotherms are also investigated.