Despite of the expanding uses of CNTs in wide verities of industrial applications, safety assessment of these materials is far less than needed. This is the first in vivo study to determine the chronic and carcinogenic effect of  double walled carbon nanotube (DWCNT) after pulmonary exposure. Rats were divided into six groups: Untreated, Vehicle, 3 doses groups of DWCNT low, middle and high and 1 dose of MWCNT-7 as  a positive control of carcinogenesis. The test materials were administrated by intratracheal - intrapulmonary spraying (TIPS) which developed in this laboratory every other days for 15 days:  DWCNT groups were administrated accumulative doses of 0.125mg/rat , 0.25mg/rat and 0.5mg/rat  and MWCNT-7 group was administrated 0.5mg/rat. Rats were observed for 2 years without further treatment. Rats were sacrificed at 52 weeks and at the end of the study at 104 weeks. Results:  The incidence of  the total lung tumors bronchiolo-alveolar adenoma (BAA), and bronchiolo- alveolar carcinoma (BAC)  (combined incidence of BAA and BAC)  in the 0.5mg group of DWCNT is 29 %  (7/24) and it is significantly higher (p<0.05) than the vehicle control group which is (1/21) and the combined tumor incidences in the three doses groups  of DWCNT is (15/75) ( 20%) (p<0.05) that is also significantly higher than the vehicle group (1/25). Neither the incidences of BAH nor combined tumor incidences were significantly high in the rats administered DWCNT 0.125mg/rat, DWCNT 0.25 mg/rat or MWCNT-7 0.5mg/rat. however, the incidence of malignant pleural mesothelioma in the MWCNT-7 group was 64 % (16/25) and it was significantly high (p<0.01) in comparison to the vehicle group (0/21) ,  DWCNT 0.125 mg group (0/25), DWCNT 0.25 mg group(1/26) or DWCNT 0.5mg group (1/24). Conclusion: It is the first study to show that DWCNT is carcinogenic to the rat lung after intratracheal administration but didn’t have much toxic or carcinogenic effect on the pleural tissue unlike MWCNT-7 which induced significantly increased  incidence of malignant pleural mesothelioma.