We present the galaxy stellar mass functions (GSMFs) and the size-mass relations down to a stellar mass of ~10^6 M_sun at z~6-9. We have identified the z~6-9 galaxies with the Hubble Frontier Fields optical and near-infrared images, exploiting the strong lensing magnification. We measure the stellar mass (M_star) of the galaxies by SED fitting to derive the GSMFs, whose mass limits are lower than than those of previous studies by >~1 dex. We compare the M_star with the sizes of the galaxies, identifying candidates of early globular clusters (GCs) whose M_star and sizes are comparable to those of the GCs in the Milky Way.