  We have investigated electronic structures of La$_3$S$_4$ and Ce$_3$S$_4$
using the LSDA and LSDA+$U$ methods. Calculated density of states (DOS) are
compared with the experimental DOS obtained by the valence band photoemission
spectroscopy. The DOS at $E_{\rm{F}}$ indicates the 5$d$ character in
La$_3$S$_4$ and 4$f$ character in Ce$_3$S$_4$. It is found to be nearly half
metallic in the ferromagnetic ground state of Ce$_3$S$_4$. %Ce$_3$S$_4$ has
ferromagnetic ground states with spin and orbital magnetic %moments of 1.27
$\mu_{\rm{B}}$ and $-$2.81 $\mu_{\rm{B}}$ per Ce, respectively, %and shows
nearly half metallic ground state. We discuss the superconductivity and
structural transition in La$_3$S$_4$, and the absence of structural transition
in Ce$_3$S$_4$.
