The environmental instability of black phosphorus (BP) is one of the difficult issues nowadays that need to be addressed urgently due to its serious degradation, damage in structure and deterioration in properties after exposure to ambient conditions, which severely limits the practical application of BP and its devices under humidity circumstances containing oxygen, particularly watery environments containing oxygen. In this study, PEDOT:PSS with high electrical conductivity, good film-forming ability, excellent environmental stability, and satisfactory solution processability was introduced to improve the environmental instability of BP with unusual structure and extraordinary properties. The mixed dispersions of BP-PEDOT:PSS with different weight ratios were successfully prepared by sonication-assisted liquid-phase exfoliation in isopropanol containing PEDOT:PSS particles under an anhydrous and oxygen-free nitrogen atmosphere. The hybrid semiconductor films of BP-PEDOT:PSS were obtained by drying corresponding BP-PEDOT:PSS mixed dispersions under vacuum; these films were then exposed to ambient air for days before their morphology, structure, and other properties were characterized. The BP-PEDOT:PSS film electrodes were prepared by drop-coating corresponding isopropanol dispersions of BP-PEDOT:PSS, and their environmental stabilities were investigated by electrochemistry in different water systems containing oxygen. The introduction of PEDOT:PSS not only enhanced film-forming ability and electrical conductivity of BP composite films, but also improved their environmental stability in water containing oxygen, which will afford a new opportunity for their application in electronics and optoelectronics of inorganic/organic polymer hybrid semiconductors based on graphene-like materials/conducting polymers under moist air conditions, particularly the electrochemical application in sensors, capacitors, and batteries/cells of BP-PEDOT:PSS composites and their devices in watery environments containing oxygen.