“Limnology” a new interdisciplinary science with multifarious dimensions has emerged which deals with the study of structural and functional attributes of the lentic fresh water environment and problems associated with them. Limnology has immense and universal significance for the citizen of today, all around the world. Streams, rivers, wetlands and lakes are home for many small animals called macro invertebrates. The term macro invertebrates describe those animals that have no back bone and can be seen with naked eyes. This study includes analysis of identification of invertebrates in Anasagar Lake in Ajmer (Raj.).The methodology employed involves collection and identification of invertebrates with the help of various equipments and tools. The result has been presented in form of a key of freshwater invertebrates of Anasagar Lake of Ajmer.