Tunable phase shifters with wide bandwidth are highly demanded for phased array radar systems. However, most wideband phase shifters are not tunable, while tunable phase shifters operate at a very narrow band. Here, we present a magnetically tunable wideband ferrite-based metamaterial phase shifter by periodically arranging ferrite block and air-gap. Compared to the conventional phase shifter, the operation bandwidth of the metamaterial phase shifter increases significantly because of the existence of a new resonant peak. Meanwhile, the phase shift of the metamaterial phase shifter can be altered by changing the applied magnetic field. The proposed phase shifter has low insertion loss and large phase shift value, which provides a way to the design of tunable wideband phase shifters.