In the last few years as the growth & use of Internet increases and share of user's opinions increases, the inspiration towards opinion mining also increases. When person wants to conduct some research or making day to day decisions, he has to depend on other people's opinions. We consult "political discussion forums when going to a political vote, read consumer reports when purchasing some products, ask friends to recommend a hotel for the stay". And now Internet has now made it possible to find out the opinions of millions of people on everything from latest gadgets to latest software. Opinion mining is a type of natural language processing for tracking the perceptions or sentiments of the public about a particular product. It can be useful in several ways in marketing. It helps to judge the success of a launch of new product. This paper gives a brief survey on the opinion mining.