In spite of it is baseline importance for comparative studies with the past and present data, an updated list of marine green algal taxa for the Biosphere Reserve of Sian Ka’an is not yet available. The aim of this paper is to present an updated list of marine green algal taxa for the Sian Ka’an Reserve based on literature and collections made by the authors in 17 localities during 2011–2012. Fifty-five taxa are new records for the study area and thus the list has increased to 129. Additionally five taxa are reported for the first time to Quintana Roo, and 11 to Mexican Atlantic coast. These results contribute to the knowledge of green seaweed diversity and also support the relevance of the Sian Ka’an Reserve as a high priority area for conservation due to their high level of algal biodiversity.