Bianchi type I magnetized cosmological models in the presence of a bulk viscous fluid are investigated. The source of the magnetic field is due to an electric current produced along the x-axis. The distribution consists of an electrically neutral viscous fluid with an infinite electrical conductivity. The coefficient of bulk viscosity is assumed to be a power function of mass density. The cosmological constant Λ is found to be positive and is a decreasing function of time which is supported by results from recent supernovae observations. The behaviour of the models in the presence and the absence of magnetic field are also discussed.