Aviadenovirus CELO is a promising vector for gene delivery to eukaryotic cells, including mammalian cells. In the present state of affairs, it gives a chance to apply recombinant adenoviruses CELO against animal pathogens. High expression level of transgene consisting of virus vector is necessary to reach protective humoral and T-cell immune answer. One of the approaches to enhance the expression level of transgene consisting of viral vectors is inclusion of addition 5'- and 3'- untranslated regulatory elements (PARS, IRES, WPRE) to the expression cassette. In this work, 5'-untranslated regulatory elements of major late transcription unit of CELO genome (a bipartite leader and gene hexon leader) were used for construction of the expression cassette consisting of the recombinant adenovirus CELO to provide high expression level of reporter gene of secreted alkaline phosphatase in nonpermissive cell system. It was shown in our experiments that the obtained recombinant adenovirus CELO was characterized by enhanced (2.4-3.5 times) expression level of reporter gene in transduced mammalian cells in vitro and in vivo.