The deal, worth 3.39 billion dollars, was signed by Iran LNG company with the Chinese consortium for an annual production of 10.5 million tonnes of LNG, the state broadcaster reported.
It did not reveal the name or give any details of the Chinese consortium.
"According to this contract, building gas liquefying lines in phase 12 and another block of South Pars gas field will be handed to the Chinese consortium," the television said. The gas field is located in the Gulf.
It added that the project would be implemented in three years and that an unnamed European firm would join the Chinese consortium in three months.
In January, Iran and China signed a separate 1.76 billion dollar contract for the initial development of the North Azadegan oil field in western Iran.
Western oil companies have refused to invest in Iran because of the controversy over its nuclear energy programme and Tehran has increasingly turned to Asian companies.
Iran holds the world's second-largest gas reserves and has significant economic ties with China — a veto-wielding member of the UN Security Council, which has imposed sanctions against Tehran over its refusal to halt sensitive nuclear work.
Iran said on Wednesday that French energy giant Total would have no "active role" in developing phase 11 of the offshore South Pars gas field and that a new partner had been found for the project.
The development of South Pars field, which holds about eight percent of world reserves, has been delayed amid a lack of investment in a country faced with severe gas needs of its own in winter.
