Inter-organizational networks represent a KIND of business cooperation and constitute a strategy to obtain competitive advantages. In this context, it has shown that effectiveness is a problematic concept. The present article seeks to contribute to the research about the effectiveness of inter-organizational networks and their explanatory factors. Based on the above, a study was performed with 45 managers of companies that make up a tourism network in Colombia, and four dimensions were measured: external resources, internal resources, intermediate results, and effectiveness, both at the network level and at organization level. The results indicate that external and internal resources of inter-organizational networks significantly predict intermediate results, as well as network effectiveness, although in a different way. In the conclusions the practical implications of the results are discussed.