Increasing potassium fertilizer rate up to 80 kg K₂O/ fed significantly increased shoot fresh and dry weights, photosynthetic pigments concentration as well as stem anatomical characters. The highest weight was obtained due to application of 40 kg K₂O/ fed in the first and seconds season as compared with untreated plants. Exogenous application of biostimulants, in particular, seaweed extract significantly increased shoot fresh and dry weights, photosynthetic pigment concentration as well as increased the diameter of stem, pith and thickness of collenchyma layers, and xylem tissue as well as the length and width of large vascular bundle beside the thickness of external phloem as compared to control in both seasons. Addition of effective microorganisms to the soil significantly increased shoot fresh and dry weight, photosynthetic pigments concentration as well as the diameter of stem, length and width of vascular bundle, and the thickness of xylem. As for the interactions, application of bostimulants, in particular, seaweed extract, significantly increased fresh and dry weights of potato shoot, photosynthetic pigments concentration as well as improved anatomical characteristics of potato stem grown under all potassium fertilizer rates with or without anaddition of effective microorganisms. The highest value was obtained under the treatment of 40 kg K₂O/fed with addition of effective microorganisms and spraying plants with 500 mg/l seaweed extract as compared with control plant in the first and second growing seasons.