Laurencia caduciramulosa Masuda et Kawaguchi, previously reported from the Pacific Ocean and from the Mediterranean Sea, is recorded for the first time for the Atlantic Ocean, at different sites in Ilha Grande Bay, State of Rio de Janeiro, southeastern Brazil. The specimens were collected as epilithic or epiphytic plants from the lower intertidal zone to 5 m depth at sheltered to exposed rocky shores during the period 2001-2005. This Laurencia species is characterized by its reduced size, well-developed stolon-like basal system and abundant deciduous branchlets at the upper portion of the erect axes that function as propagules. As described in other reports of this species, gametangia and sporangia were not observed. The absence of reproductive structures could be efficiently replaced by a strategic mechanism such as vegetative propagation by these propagules. This study expands the geographical distribution of L. caduciramulosa to the southwestern Atlantic Ocean, suggesting its recent introduction into Brazilian coastal environments by transoceanic shipping.