Adsorption isotherms of ethane in slit pores of a single-plane wall model at 298 K and 323 K, from low to high pressures, are calculated by use of the Gibbs ensemble MC method. The two-site Lennard-Jones model (SS model) was used in the calculations by slightly adjusting the parameters of Jorgensen et al. (1984) to fit the experimental and calculated values of both vapor pressure and saturation liquid density of ethane near the critical point. The adsorption isotherms calculated from the SS model and those from the spherical LJ model, are found to be almost the same in shape and magnitude though slight differences are observed. That is, the maximum adsorption capacity of the SS model is slightly larger than that of the LJ model while the LJ model gives higher adsorption in the low-pressure region. The local density and orientational ordering of the dumbbell molecule of the SS model in slit pores are calculated. The molecular orientation to the surface is suggested to be sensitive to the ratio of the slit width and the site diameter.