The equiatomic SnBi alloy was studied by X-ray angular-dispersive diffraction using a diamond anvil cell up to a pressure of 15 GPa. The first transformation at 1.5 GPa from the eutectic phase mixture (Sn + Bi) to a single phase state (X-phase) confirms earlier work. This is followed upon an increase in pressure to 10.5 GPa by a new transformation to a body centered cubic, bcc, structure. All transformations are reversible upon a decrease in pressure. Structural properties of SnBi alloy under high pressure are discussed in connection with the known high pressure forms of the constituent elements, and the possibility of extended bcc solid solutions is suggested.