Abstract: The invention relates to novel chimeric adenoviruses comprising the type 5-modified chimeric adenoviruses, in which the fiber knob domain in the adenoviruses type 5 is replaced by the adenoviruses type 35 fiber knob domain and any exogenous transcriptional regulatory regions controlling expression of the E1A and E1B genes are introduced into the region from which adenoviruses type 5 E1A transcriptional regulatory region has been removed. The chimeric adenoviruses are cytotoxic or oncolytic chimeric adenoviruses and can be utilized as, for example, pharmaceutical agents having high cytotoxic activity against intractable tumors such as malignant mesothelioma.