Although the term Mental Accounting sounds strange to many people but knowingly or unknowingly every people is aware about mental accounting. Every human being allocates their budget mentally before attempt a purchase. Mental accounting plays a decisive role in purchase decision making. Thus after considering this psychological fact of people, the present study tries to explore the importance of mental accounting in purchase decision. The present study doesn’t confine to only exploration of importance of mental accounting in purchase decision but also tries to place mental accounting as a vital stage in buying decision making process. The findings of such a study is expected to hold much importance in better understanding the basic and analytical manner in which the customers’ minds work while deciding on their purchases; which, in turn, would be helpful in developing various marketing strategies in respect of timing of offers, pricing, payment aids, product launches, transaction facilitation, so on so forth. Moreover, this paper tries to add some more ingredients in mental accounting theory which was propounded by Richard H. Thaler.