Centuries ago, there were some small scale real estate agency firms in Hong Kong. Many of them were small scale family business. As large scale shopping malls were uncommon at that time, these shops were opened on the streets. Nowadays, the market structure of real estate agency sector is an oligopoly. Ricacorp, Centaline, Century 21, Midland Realty, and Hong Kong Properties are the five major large-scale agency companies in Hong Kong. In the modern era, many of these agency firms open their branches inside the shopping malls beneath the large scale residential estates. To better understand the reasons for this phenomenon in Hong Kong, we have conducted two case studies. The case study of Ricacorp, one of the large-scale real estate agency firms in Hong Kong, shows that over half of the Ricacorp real estate agencies shops are opened in shopping malls that are owned by the major developers in Hong Kong. The second part of the case study explores some of the major shopping malls in Tseung Kwan O, a new town in Hong Kong. We find that many shopping malls have similar “content” and appearance because they have similar branded shops. Secondly, the agency firms also open their shops in different malls owned by the same developers. We therefore propose that the oligopoly market structure is caused by two factors: 1) lower transaction costs are incurred when the large scale agency owners negotiate with the mall owners in settling the terms of contracts: A) the mall owners do not need to draft separate contracts for the different agency companies. One piece of contract (or more or less the similar terms of contracts) fits all the agency branches owned by one single firm. B) there is no need to search for background information on each company if the shopping malls are contracting with a single agency company. C) By looking at the other shopping malls, the shopping mall designers can gather information and predict the success of the tenant mix easily. 2) Modern shopping centres usually locate below the towers of residential buildings. By opening the agency firms inside these malls, the consumer’s search costs can be lowered. Despite both the small and large scale agency firms know that these shopping malls can help them secure better business returns, the large-scale companies can easily build up closer relationships with the mall owners (due to factor 1) find it easier to rent their units at a lower rent while the smaller firms find it hard to expand in the New Town’s shopping malls. These small firms are forced to stay in lower profit margin regions in old estates where there are only street shops without large scale developer’s renting administration. Therefore, it is sufficient to conclude that the shopping mall has imposed a relative higher costs to new comers should they wish to enter the real estate agency market in new town area.