Abstract: Experimental and theoretical studies on the shape of a single bubble in downwardly inclined gas-liquid two-phase flows are carried out.Measurements of the shape are made using conductance probes and visual observation in this paper.The experimental results show that bubble turning phenomenon of bubble shape happens at low Froude number,which is defined by gas/liquid mixture velocity.The turning phenomenon significantly affects the bubble velocity.It is also found that the shape of bubble is mainly determined by the Froude number rather than the bubble length.A hydrodynamics model for the shape of bubble tail is de-rived based on a one-dimension two-fluid model.The model well predicts the characteristics of the bubble tail when compared with the experimental results.The theoretical analysis shows that the critical Froude number,at which the turning phenomenon happens,increases as the downward inclination and pipe diameter increase.