Ottawa is the capital city of Canada. In the previous cross Canada radon survey, Ottawa was not included. There is great interest to know radon level as well as thoron concentration in Ottawa homes. Therefore, radon/thoron discrimination detectors developed at the National Institute of Radiological Sciences in Japan were deployed in 93 houses for a period of 3 months. As expected, thoron is present in Ottawa homes. Radon concentrations ranged from 8 to 1525 Bq m(-3) while thoron concentrations varied from 5 to 924 Bq m(-3). The arithmetic mean of radon and thoron concentrations were found to be 110 +/- 168 and 56 +/- 123 Bq m(-3), respectively.