For the first time, the bryoflora of the Pontifical Villas of Castel Gandolfo (Vatican City State) has been studied. Research led to the identification of 87 bryophytes (1 hornworts, 15 liverworts and 71 mosses), among which one liverwort and six moss species are new reports for the Lazio Region. Zygodon forsteri, epiphyte species considered Vulnerable in Europe, Anthoceros agrestis and other species rare for Italy, were found in the study area. In addition, the life-form of each species was taken into consideration, in order to compare with the ecological and climatic characteristics of the territory examined. The study contributes to the knowledge of a territory of the Vatican City State that until now had been almost unexplored from the bryological point of view and provides important information for the realization and definition of the European and Mediterranean Red List of Bryophytes.