Agricultural product market is spatial market in which the producer and the consumer are distributed at different locations. The Law of One Price (LOP) would reduce the risk, increase production and income, food security, social welfare and affects on income distribution. The purpose in this research has been to analyze the LOP via continuity and to evaluate the types of continuity among five selected farm products within nine main cities, as well as for the whole products in the agricultural sector. Monthly statistical data during 1982-1999, (including 10000 items) is used. In order to test the main hypotheses, we have applied the Ravalion model using stationary data. The results have shown that in most cases the strong continuity and short term continuity is rejected. Thus, farm products market are far from ideal. Long-run continuity is estimated to be about 39 percent. The type of relationships between markets is from price setter to price taker; in all markets but onion, the producers market dominates the prices. Identification of this dominant markets would help the policymakers to monitor the markets within the right ranges. This in turn would reduce costs and accelerate the effects of agricultural policies. According to the results obtained, we would suggest to analyze the agricultural product markets in Iran, using imperfect competition structure