Fungi are responsible for the majority of postharvest diseases of fruits, which cause large postharvest losses. Active films are promising delivery systems for ingredients with bioactive properties, allowing for the improvement of food quality and safety. The present study aimed at producing essential oil of Chenopodium ambrosioides (EOCA), as well as developing active films incorporated with different concentrations of EOCA (0, 100, 200, 300, and 400 g kg–1). EOCA increased the films' opacity, solubility, and extensibility while decreasing rigidity, resistance, and permeability to water vapor. Cellulose acetate provides a slight thermal stabilization of the EOCA. The active films were effective against the phytopathogens Fusarium oxysporum and Colletotrichum gloesporioides in the vapor phase. The active films containing EOCA were successfully obtained, and, according to the results, we can emphasize the potential application of the films developed as active food packaging, highlighting the postharvest preservation of fruits and vegetables.