Complex-valued models have been applied to several fields as a result of their advantages in modeling and processing uncertain information, but few studies have addressed the uncertainty associated with them. It is therefore the main contribution of this paper to propose a complex-valued Deng entropy in the complex-valued evidence theory (One of the complex-valued models). Complex-valued Deng entropy effectively measures the uncertainty of the mass function in the complex-valued framework. It involves uncertainty related to phase angle information, inconsistency and non-specificity. Additionally, complex-valued Deng entropy is a generalization of the Deng entropy and Shannon entropy. In other words, complex-valued Deng entropy may collapse to classical Deng entropy if the complex-valued mass function collapses to a mass function in real space. If the complex-valued mass function collapses into the probability distribution in real space, the complex-valued Deng entropy also collapses into Shannon entropy. There are also a number of numerical examples illustrating the compatibility and effectiveness of the complex-valued Deng entropy. Finally, this article presents a classification experiment involving entropy. Results of classification experiments indicate that results associated with the core parameter of complex-valued Deng entropy are more accurate than results associated with the core parameter of Deng entropy in some data sets.