The aim of this paper is analyzing the role of psychology of numbers in financial markets and in this area, investigates the Price Clustering phenomenon in trading prices of Tehran Stock Exchange. Price clustering is one of anomalies that have been observed in financial markets that representative psychological biases or tendency to specific numbers in the market. This phenomenon includes of density of prices in specific numbers or rounding the prices. This research is done in the period of 77 to 89 (including three period of 77-80, 81-84 and 85-89), that survey substantial daily prices.
The results of the paper confirm the existence of price clustering. The results show that in Tehran Stock Exchange, tendency to trading at round numbers is intensive and tendency to numbers of 5 and 9 is to some extent more than others. For other numbers this tendency is almost similar and there are uniform distributions for them. Also attraction hypothesis, as one of the explanations of price clustering is accepted. Furthermore, this research is rejected the resolution hypothesis for explaining the price clustering phenomenon in Tehran Stock Exchange. Results of creation and comparison of portfolios are show that there isn't a significant relation between price clustering and stock prices, size of firms, Liquidity of stocks and volatility of prices.