Floating Modular Energy Islands (FMEIs) are modular floating structures which combine different types of renewable energy production systems. FMEIs are still at their conceptual phase; however, they promise good potential for using the limited ocean space in an efficient way to produce renewable energy. Since those systems would have different components and related materials, offshore construction/installation work and systems to transport generated energy to land, their environmental sustainability is an important aspect to evaluate, as for other existing marine renewable energy systems. Life cycle assessment (LCA) is a scientific, standardized and quantitative methodology for the evaluation of environmental sustainability and it is accepted to be compatible for the evaluation of marine renewable energy systems. This study focuses on previous applications of LCA on various marine renewable energy systems, which have the potential of being a component of a floating modular energy island. With this aim, a brief literature review on possible different components of energy islands is conducted. Offshore wind energy, tidal energy systems, wave energy converters, floating solar energy and hydrogen energy are selected to be reviewed in the study. For the literature review, a common literature screening methodology is developed with a similar keyword group except the marine renewable energy type considered. Selected papers in each energy type production technology are reviewed with reference to the main phases of a LCA study: Goal and Scope Definition; Life Cycle Inventory (LCI); Life Cycle Impact Assessment (LCIA) and Interpretation. Under each subtitle, the approaches followed are assessed covering the important aspects, methodology/criteria considered, and challenges encountered. By this way, it is aimed to generate knowledge on the LCA methodology as a guideline for the FMEIs.