ExpiCHO is a highly efficient transient expression system that provides an expression level comparable to stable cell lines within two weeks. While CHO cells have been widely used in the industry for a long time, stable cell lines must be constructed to obtain CHO-expressed proteins, a time-consuming and labor-intensive procedure that requires experienced R&D personnel. In the drug development phase, it is necessary to produce a large quantity of proteins in a relatively short period of time, which makes the 293-transient expression system the only choice in most cases. This system, however, expresses at low levels with inconsistencies in the quality of the yielded proteins compared with the CHO system. In contrast, ExpiCHO, as an efficient transient expression system, can reach a yield of at least 1 g/L in just two weeks. In 2017, we used this system for the production of multiple fusion proteins and monoclonal antibodies. The expression levels were maintained at 1 g/L or more, exceeding 2 g/L and up to 3 g/L in some cases. When comparing the expression levels of the transient expression platform with those of stable CHO-S cell lines, we found that the two systems were similar. In addition, while expressing a large amount of a protein, the transient system could also evaluate the expression level of the molecule in stable cell lines. ExpiCHO therefore provides an excellent tool for users who need to prepare a high volume of proteins rapidly.