Two field experiments were carried out during the two successive summer seasons of 2016 and 2017 at a private farm near Kafr saad center, Damietta Governorate, Egypt to study the impact of NPK fertilization at (100%, 50% and 0% NPK of the recommended doses) and some bio-stimulants (without, effective microorganisms (EM) 2ml/L, microbial mixture 1L/20L, yeast extract 10g/L and seaweed extract 1g/L) as well as their interaction on yield and its components and quality parameters of sweet potato plants Abees cultiver. Obtained results showed that increasing NPK fertilization levels from 0% to 100% of the recommended doses gave significant increments in total yield/fed, dry matter and quality parameters i.e. crude protein (%), total carbohydrates (%), starch%, total sugar %, beta-carotene and vitamin-C (vit.c) in tuberous roots of sweet potato in the two seasons. All bio-stimulants treatments increased significantly of all the previous mentioned parameters and decreased nitrate and nitrite contents in tuberous roots compared with untreated plants, EM gave the best values of all studied parameters. Doses 100 % and 50 % NPK plus EM gave the best significant increases in the studied parameters in both seasons and the interaction between 0% NPK plus EM decreased significantly nitrate and nitrite contents in the both seasons.