The protection of persimmon fruits (Diospyros kaki L.) from postharvest fungal infestation with Alternaria alternata (A. alternate; black rot) is a major agricultural and economic demand worldwide. Edible coatings (ECs) based on biopolymers and phytocompounds were proposed to maintain fruit quality, especially with nanomaterials’ applications. Chitosan nanoparticles (NCt), rosmarinic acid bio-mediated selenium nanoparticles (RA/SeNPs) and their composites were produced, characterized and evaluated as ECs for managing persimmon black rot. The constructed NCt, RA/SeNPs and NCt/RA/SeNPs composite had diminished particles’ size diameters. The ECs solution of 1% NCt and NCt/RA/SeNPs composite led to a significant reduction of A. alternata radial growth in vitro, with 77.4 and 97.2%, respectively. The most powerful ECs formula contained 10 mg/mL from NCt/RA/SeNPs composite, which significantly reduced fungal growth than imazalil fungicide. The coating of persimmon with nanoparticles-based ECs resulted in a significant reduction of black rot disease severity and incidence in artificially infected fruits; the treatment with 1% of NCt/RA/SeNPs could completely (100%) hinder disease incidence and severity in coated fruits, whereas imazalil reduced them by 88.6 and 73.4%, respectively. The firmness of fruits is greatly augmented after ECs treatments, particularly with formulated coatings with 1% NCt/RA/SeNPs composite, which maintain fruits firmness by 85.7%. The produced ECs in the current study, based on NCt/RA/SeNPs composite, are greatly recommended as innovatively constructed human-friendly matrix to suppress the postharvest destructive fungi (A. alternata) and maintain the shelf-life and quality of persimmon fruits.