Among the essential activities of banks to benefit their clients and themselves is the allocation of resources. One of the essential aspects of resource allocation is determining the optimal combination of payment facilities to various economic sectors. In this article, using the post-modern portfolio theory approach (the Mean-semi variance approach), the optimal portfolio of shared facilities of Iranian commercial banks is determined. The average monthly stock return of the companies operating in each sector (during 2008 to 2011) is used as the return rate of each sector. Results indicate that, in order to have minimum variance or the maximum risk aversion, participatory facilities should be allocated as follows: 33% to the industry sector and mining, 22% to the housing and building sector, and 29% to the agricultural sector. Also commercial and service sector are allocated 16% of the facilities which is relatively risky, so that with an increase in the risk acceptance of the banking system and at the expense of decreased share of facilities in the industrial, mining, and housing sector, the optimum share will increase to 26% and then decrease with further increase in risk acceptance rate.