The superconductivity of ß-(BEDT-TTF)2trihalides is discussed based on the experimental results on the pressure effect on resistivity and on Fermi surface. We examine anion-alloyed ß-(BEDT-TTF)2trihalides how the temperature dependence of resistivity changes with pressure. We find that the temperature dependence of resistivity is distinctively classified between those that exhibit superconductivity and those that do not. The low temperature resistivity of the superconducting samples decreases with pressure with almost the same rate as that at room temperature, while the low temperature resistivity of the non-superconducting samples does not change with pressure. This is also true with the recent 10 K-superconductor, κ-(BEDT-TTF)2Cu(NCS)2. Second topic of this paper is of the Shubnikov de Haas effect on ß-(BEDT-TTF)2I3 and ß-(BEDT-TTF)2IBr2. The area of the Fermi surface are found to be 1 4 of the first Brillouin zone contrary to the expected value of 1 2. We discuss the structure of the Fermi surface of these materials and other isostructural salts.