The trend to centralise the competences in the Spanish State does not escape the field of environment nor the environmental assessment. Ensuring market unity, security and other legal arguments have served as an excuse to enact legislation towards harmonization of regulation. Hence the enactment of laws of basic character with a detail of treasury of a regulation that leave little room for maneuver to the CCAA unless they decide to enact additional protective regulation. In practice, this entails a reduction in regional powers, an involution of political autonomy and in the decentralization of the Spanish State. The current basic state law 21/2013, of December 9, environmental assessment has led the involution. In this paper we analyse the consequences of this legislation in the autonomous powers on theenvironmental impact assessment of projects. For this we have studied the basic rule itself and the regional EIA regulations, focusing in those new aspects of the regional legislation regarding basic legislation. Finally, in conclusion, recommendations and proposals in relation to the experimental question are provided.