Abstract: This research analyses the impact of public regulation on the efficiency of the Spanish Ports Authorities during the last three decades. To this end, using Stochastic Frontier Analysis(SFA), an input-oriented distance model has been estimated for a sample of 26 Port Authorities during the period 1986-2012.This paper contributes to the literature by establishing a direct co relation between the reform and the change inefficiency. Four regulatory changes have been carried out in the Spanish port system during the last three decades: Act27/1992, Act62/1997, Act48/2003 and Act33/2010. In line with other reforming countries around the world, the regulatory reforms rested on three key instruments: decentralization (port autonomy), participation of private sector and introduction of competition. This paper supports that Act62/1997 and Act48/2003 focused on the promotion of port autonomy, privatisation and inter-port competition and had a positive impact on the efficiency of the Spanish port system