The five leaders signed agreements on trade and economic cooperation, cooperation in the transport sector.
Speaking to reporters before flying to Aktau, Rouhani said the Caspian summit is of great significance, as it would make decision on a long-awaited principal convention.
The legal status of the Caspian Sea, the world's largest inland body of water, had been unresolved since the 1991 collapse of the Soviet Union.
Russia, Iran, Kazakhstan, Turkmenistan and Azerbaijan signed the Convention on the Legal Status of the Caspian Sea in the Kazakhstan city of Aktau on Sunday.
Nevertheless, Rouhani hailed a stipulation in the convention that prevents non-Caspian countries from deploying military forces on the sea.
There are some 50 billion barrels of oil and almost 9 trillion cubic meters of gas in proven or probable reserves in the Caspian seabed.
Berdimuhamedov said the convention will promote mutual understanding between coastal countries and added Caspian Sea will permanently remain the zone of peace and good-neighborliness. In addition, the environmental factor should be taken into account in the implementation of large-scale offshore projects, and all parties are responsible for damage to the ecological system of the Caspian Sea.
If it is treated as a sea, then it would be covered by worldwide maritime law, namely the United Nations Law of the Sea.
While the agreement today settled the status of the sea's surface and created a formula for dividing the subsea resources, the delineation of new borders could prove contentious.
The treaty ends a spat over whether the Caspian is a sea or a lake, granting it special legal status and clarifying the maritime boundaries of each surrounding country.
It's estimated there are 50 billion barrels of oil and almost 8.4 trillion cubic metres of natural gas beneath its seabed.
Nazarbayev said the convention allows for the construction of underwater oil and gas pipelines as well as setting national quotas for fishing and forbids any foreign military presence. The Trans-Caspian Pipeline (TCP), from Turkmenistan to Azerbaijan, has been opposed by both Russian Federation and Iran.
The problem is that the Caspian Sea is a unique body of water in the world, and so there are no examples to provide guidance.
Sunday's agreement potentially opens the sea for underwater oil and natural gas pipelines, which Russian Federation had opposed, ostensibly on environmental grounds, though it has built such pipes in the Black and Baltic seas. "We also have signed a series of agreements", President of Kazakhstan Nursultan Nazarbayev said.