Conditionally-replicating adenoviruses (CRAd) are becoming a promising strategy for cancer therapy. However, the generation of CRAd is complicated and time-consuming, especially for armed CRAd Ad5-D24. A one-step ligation system is now reported for rapid construction of an armed CRAd Ad5-D24 carrying two foreign transgenes. The system has the following features: (1) the CRAd backbone pCRAd5-D24-BS-Lacza contains two unique restriction sites between the fiber and E4 for easy introduction of a transgene expression cassette; and (2) a bi-directional promoter in pshuttle-BS-Dual allows for the expression of two independent transgenes. As proof of principle, Ad5-D24 CRAd carrying eGFP and mCherry was generated and examined. This novel ligation system will be a versatile and efficient tool in cancer viral gene therapy.