  We investigate the extinction curves of young galaxies in which dust is
supplied from Type II supernovae (SNe II) and/or pair instability supernovae
(PISNe). We adopt Nozawa et al. (2003) for compositions and size distribution
of grains formed in SNe II and PISNe. We find that the extinction curve is
quite sensitive to internal metal mixing in supernovae (SNe). The extinction
curves predicted from the mixed SNe are dominated by SiO2 and is characterised
by steep rise from infrared to ultraviolet (UV). The dust from unmixed SNe
shows shallower extinction curve, because of the contribution from large-sized
(~ 0.1 um) Si grains. However, the progenitor mass is important in unmixed SNe
II: If the progenitor mass is smaller than ~ 20 Msun, the extinction curve is
flat in UV; otherwise, the extinction curve rises toward the short wavelength.
The extinction curve observed in a high-redshift quasar (z=6.2) favours the
dust production by unmixed SNe II. We also provide some useful observational
quantities, so that our model might be compared with future high-z extinction
curves.
