In Qajar era, the importance of commercial function of Mazandaran province to sovereignty was considerable due to its position. In fact, Mazandaran had a strategic position for government regarding two reasons; the first reason is that it was the nearest rich province to Tehran-capital of Iran-in foodstuff production and second one is that the closest trade link of Tehran to Caspian Sea, which was the route of Iran's trade with Russia _ the largest trading partner of Iran– passed through this province. Moreover, Mazandaran had a comparative advantage in the production of some exported crude stuffs such as rice, cotton, silk and wood. Consequently, the expansion of Mazandaran roads could be considered an important factor in developing of economy in the local, regional and national scales. In Naser al-Din Shah Period, Despite of all political, economic and geographical difficulties in expanding of Mazandaran's roads, government decided to spend a huge capital in the expansion of Larijan road considering the protection of political and economic security of the capital city according to a number of preliminary studies conducted by a group of engineers on three available routes including Hezar Cham, Larijan and Savadkuh. The present research endeavors to investigate the effects of road construction programs of Naser al-Din Shah on the trade of Mazandaran province based on statistical data and using diagrams with descriptive-analytical approach. The outcomes of this research reveal not only the substantial role of road construction in increasing of exports and imports of Mazandaran province but also its impact on Mazandaran's commercial changes such as the increase of commercial caravansaries and the growth of markets of Barforush, Sari and Ashraf cites.