The three-month tests of 137 island homes, 73 in Guernsey and 64 in Jersey, measured the level of gas in the walls.
Radon occurs naturally in areas with a large amount of granite and 99 of the homes tested were below target levels.
Fourteen island homes were above the target level and owners have been told to ensure there is good ventilation.
The survey was carried by the islands' authorities with the UK Health Protection Agency. The 137 properties were selected to cover a range of geological conditions and population areas.
The aim was to find out more about radon and its distribution.
Val Cameron, the Channel Islands strategic lead for environmental health, said: "The recent survey updates and confirms the information from previous surveys; this is that radon is associated with the granite geology of the island, and not the construction material of an individual building."
International research has found exposure to radon gas can increase the chances of contracting lung cancer for people who smoke.
Dr Susan Turnbull, medical officer of health for Jersey, said: "To help put the main risk factors for the commonest form of lung cancer into perspective, for every 100 cases of lung cancer around 95 will have been caused by smoking alone, about four will be due to the combined effects of smoking and radon exposure.
"Only one will be due to radon exposure alone. So it is a real risk, albeit a low one. The most sensible thing anyone can do to reduce their risk of getting lung cancer is to stop smoking."
Mrs Cameron said: "Of the homes surveyed, some were identified as being above the action level. Advice has been given to those householders about measures to remedy the problem."
Previously radon surveys were carried out in Jersey in 1987, 1992 and 1997, and in Guernsey in 1985. In 2012, tests were also carried out in Herm, Alderney and Sark.
In 1984 the Royal Commission on Environmental Pollution and the International Commission on Radiological Protection reported on the need for a reduction of radon exposures in homes.
The amount of radon gas found in the Channel Islands is associated with the geology of the island and not construction materials, a survey finds.