The term “Entity Extraction” is a renowned technique now and broadly employed as a part of opinion mining and sentiment analysis. This technique is one of the information retrieval approaches, where the precise data have been obtained from the huge volume of information resources. Entity extraction is a traditional approach of named entity extraction, which is basically, retrieves the person name, product names, organization names, services, political issues titles, news article titles, locations and local and global time and etc. This entity extraction is very interesting filed and plays a major role in bio-medical field to recognize the drug entities, understand biological data in bioinformatics and categorize bio-medical documents, document summarization and explore the bio-medical terms and etc. Since the volume of online data has been increasing day by day, the entity extraction process needs more efficient techniques to find the entity replication, document replication, semantics between entities and documents and etc. This paper presents a study of various approaches employed in entity extraction on unstructured data. © 2016, International Journal of Pharmacy and Technology. All rights reserved.