Carbon nanotubes (CNTs) have been synthesized and produced on large scale for their wide application. They have high absorption ability to organic contaminants (such as benzene) and can form CNTs-benzene combination with benzene. In this article, the acute pulmonary toxicity, induced by multiwall carbon nanotubes (MWCNTs), benzene, and their combination, was studied by administrating the three test materials into mice lungs via intratracheal instillation. The biochemical parameters in bronchoalveolar lavage fluid (BALF) and pathological lesions in lungs were used as endpoints to evaluate the pulmonary toxicity of the three test materials at 3-day and 7-day postexposure, respectively. After the mice were intratracheally instilled with MWCNTs, benzene and MWCNTs-benzene combination at doses of 6.67 mg/kg, 2.67 mg/kg, and 9.34 mg/kg (containing 6.67 mg/kg MWCNTs and 2.67 mg/kg benzene), the total protein, alkaline phosphatase (ALP), acid phosphatase (ACP), and lactate dehydrogenase (LDH) in BALF and pathological lesions in lungs were examined. At 3-day postexposure, MWCNTs induced obvious pulmonary toxicity and benzene only induced slight pulmonary toxicity, whereas their combination induced very severe pulmonary toxicity. At 7-day postexposure, MWCNTs and benzene did not induce pulmonary toxicity individually, whereas their combination still induced severe pulmonary toxicity. These data indicated that, at the instilled doses in this experiment, the MWCNTs can alone induce acute pulmonary toxicity in mice and the benzene does not induce pulmonary toxicity, but the pulmonary toxicity of MWCNTs is enhanced after they form MWCNTs-benzene combination with low dose of benzene. The enhanced pulmonary toxicity may be due to the change of MWCNTs aggregation ability after benzene is adsorbed on them.