The aim of the study conducted in 2018–2020 was to determine the effect of biostimulants and herbicide Avatar 293 ZC on the occurrence of external and internal defects and small tubers in the potato yield. The edible cultivars evaluated were Oberon and Malaga and biostimulants used: PlonoStart containing prolactic acid bacteria, actinomycetes (N-16.4%, K2O-0.75%, CaO-0.07%, MgO-0.02%, S-941 mg·kg−1), Aminoplant containing free amino acids-11.57%, organic matter-87.7% (Ntotal-9.48%, Norganic-9.2%, N-NH4-0.88%, Corganic-25.0%), and Agro-Sorb Folium including total amino acids-13.11%, free amino acids-10.66% (N-2.2%, B-0.02%, Mn-0.05%, Zn-0.09%) with herbicide (clomazone and metribuzin): objects 3,4 and 5 and a single herbicide (object 2), as well as a control object (1). Before harvesting, tubers were collected from 10 randomly selected plants from each plot. The yield structure was determined in these samples - the weight share of tubers below 35 mm, 36-50, 51-60 and above 60 mm. Tubers with a diameter of less than 35 mm are classified as small - non-commercial tubers. Tubers with a diameter above 35 mm constituted the commercial fraction, in which external and internal defects were determined. The sum of tubers with defects and small tubers constituted side yield. The using of all biostimulants with herbicide significantly reduced: the share of tubers with defects, the share of small tubers in the yield and the total weight of small tubers and tubers with defects compared to the control plant. The best effects in reducing the occurrence of tubers with external and internal defects and small tubers were obtained by using the Agro-Sorb Folium and herbicide. Among the cultivars, Malaga cv. turned out to be more resistant to defects and the production of small tubers than the Oberon cv. In the literature, especially foreign, there are sporadic studies on the effect of biostimulants on the occurrence of defects in potato tubers.