Ytterbium borosilicide YbB 4 5 . 6 Si 1 . 0 crystals were successfully grown by the floating zone method. YbB 4 5 . 6 Si 1 . 0 takes the recently discovered YB 5 0 -type structure and has an orthorhombic structure with lattice constants of a=16.636(4) Å, b=17.644(2) Å, c=9.488(2) Å. Other magnetic REB 5 0 -type compounds have been discovered to exhibit the first magnetic transitions found for B 1 2 icosahedral compounds. The physical properties of ytterbium borosilicide were investigated to observe whether anomalous behavior is observed for the ytterbium phase such as is the case in the REB 1 2 borides where YbB 1 2 is a Kondo insulator. The resistivity of YbB 4 5 . 6 Si 1 . 0 follows the 3D variable range hopping temperature dependence down to low temperatures. The existence of sizable magnetic anisotropy is indicated and anomalies are observed at low temperatures indicative of a magnetic transition of antiferromagnetic character with T N =5.5 K. This behavior is similar to that of the other magnetic REB 5 0 compounds. Information on the electronic ground state is also obtained, with the ground state of ytterbium borosilicide indicated to be a Kramer's doublet.