The SQUID measurements revealed an antiferromagnetic transition of kappa -B
ETS2FeBr4 around 2.5 K (BETS=bis(ethylenedithio)tetraselenafulvalene). Resi
stivity measurements showed an anomaly at T-N which gave a clear evidence f
or the interaction between pi metal electrons and localized magnetic moment
s in organic metal system for the first time. A superconducting transition
was observed at 1.1 K. The specific heat indicates the coexistence of antif
erromagnetism and superconductivity below T-c. Similar successive antiferro
magnetic and superconducting transitions were observed in kappa -BETS2FeCl4
. A superconducting transition was observed also in lambda -BETS2FeCl4 at h
igh pressure.