Cittaslow is a network of small cities which have adopted the assumptions of the “slow city” model and strive towards the improvement of the quality of life for their residents. This is a network of cities which put pro-social and pro-environmental measures in the first place, while ensuring that the unique character of every city is preserved. A city which wishes to join the Cittaslow network must go through the so-called certification process and satisfy a number of criteria classified in seven macro-areas, including the “energy and environmental policy” area. Significantly, after becoming a member of the network, the city is obligated to carry out activities that will enable it to meet the membership criteria to a higher degree, and in particular to satisfy the criteria it has previously failed to meet. Considering the above, the aim of this study has been to evaluate the activities initiated and implemented by the member cities of the Polish Cittaslow network in the sphere of the “energy and environmental policy”. A comparative analysis was made of the results of certification before entering the network and the results of recertification that each city underwent after five years of its membership. The study shows that, even in the first five years following their access to the network, the cities were able to implement many projects dedicated to the protection of environmental, reduced consumption of electricity and use of alternative energy sources as well as improvement in the ecological awareness of city inhabitants. This is reflected by a higher degree to which these cities meet the certification criteria in this field, from 71% to 75%.