This paper experimentally investigates effects of speeding-up inlet on rotational speed of marine current energy turbine. Several length-radius ratios L/d and area ratios A´/A of the speeding-up inlet as well as several flow yawing angles θ were considered. Also, a comparison of rotational speed of turbine in the presence and absence of speeding-up inlet was made. A relation between flow velocity V and rotational speed of the inlet n was analyzed. And a relation between flow velocity and rotational speed of turbine in free stream was theoretically developed.