A wide range of physical properties of liquid Co-based alloys has been investigated. The temperature dependencies of kinematic viscosity have shown to be non-monotonic. The correlation between the viscosity and some magnetic properties of amorphous ribbons has been established. Higher viscosity of the melt leads to better magnetic properties: higher maximum permeability, lower coercive force. The re-melting leads to increasing of the magnetic properties of produced ribbons. The optimization of temperature regime of melt preparing before amorphization has been proposed.