Purpose - This paper aims to investigate the specific challenges and success factors faced by companies which develop their environmental corporate reputation using an online communication strategy. Design/methodology/approach - The study proposes a research framework positioned to an intermediary level between quantitative research and case studies. The exploratory methodology adopted in this study was based on a triangulation approach, by comparing and analysing primary data obtained from three different sources: observations of corporate websites, data provided by the communication managers of five investigated firms, and the answers obtained from a sample of 84 environmentally-conscious consumers. Findings - The findings indicate the importance of a direct correspondence between the strategic objectives defined by the firm, the communication strategy, and the implemented operational elements. However, as a result of opportunistic environmental claims made by other firms in the past, customers require not only clear and updated online information, but also objective proofs about the trustworthiness of the company's messages and actions. Research limitations/implications - The sample of investigated firms is too small to allow a valid generalisation of results. On the other hand, the primary data was collected in only one time instance, although the process of corporate image change and reputation building is continuous and dynamic. Originality/value - Previous research focused almost exclusively on corporate environmental reporting of large companies. Adopting an exploratory approach, this paper analyses the communication strategies designed and implemented by five medium-sized French firms, as well as their impact on customers' perceptions.