Based on the theoretical background of the link between countries’ transparency and environmental policy our paper provides empirical evidence for a sample of 68 countries for the time period of 2001-2010. By assuming that countries’ transparency levels shape their environmental policy which reflects upon their environmental performance levels, we develop an empirical model for investigating such a relationship. By modifying a conditional directional distance function model, we incorporate on the measurement of countries’ environmental performance the effect of their public sector transparency levels. The empirical results indicate that public sector transparency has a statistically significant impact on countries’ environmental performance with the relation in the case of emerging-developing economies appearing as an inverted ‘W’ shape, whereas in the case of advanced-developed economies indicating an inverted ‘U’ shape.