It is well known that agrotehnical and ampelotechnical procedures have great impact to oenological quality of grape and wine. Partial defoliation is one of the most commonly used ampelotechnical procedure in canopy manipulation. The aim of this study was to evaluate the influence of partial defoliation on the yield and chemical composition of grapes Merlot in 2017. This research is based on the results obtained after partial defoliation of four basal leaves from each shoot of experimental vines carried out in four different stages; before fertilization and flowering (DI), immediately after fertilization and flowering (DII), in the faze of berry set (DIII) and in the period of veraison (DIV). In all four stages there was a reduction of yield compared to control (K), treatment where no defoliation was performed. On the contrary to the expected, there was no increase in sugar concentration in grapes after partial defoliation, while defoliation in the stage before fertilization and flowering (DI) resulted in reduced grain soluble solids concentration. Partial defoliation conducted immediately after fertilization and flowering (DII) was found an increase in total acidity and pH decrease, while in other defoliation periods (DI, DIII and DIV) there was a decrease in total acidity and pH increase. Concentration of polyphenols of partial defoliation was significantly higher compared to control (K).