The aim of the study is to determine the changes in the composition and antimicrobial properties of black mulberry, which is known to have therapeutic properties, during the processing of fruit juice and with heat treatments. The study was carried out in two parts, and it was aimed to determine the antifungal and antibacterial activity of the samples by agar well diffusion method. In order to determine the antimicrobial activity in black mulberry juices; Candida albicans (ATCC 10231), Candida lipolytica (Ankara University, Food Engineering Department Culture Collection, AUGMKK), Candida parapsilosis (Refik Saydam Culture Collection, RSSK 03025, Lausanne 994), Candida krusei (RSSK 610), and Saccharomyces cerevisia (AUGMKK) were used as test microorganisms from filamentless microfungi. In addition to fungi, Staphylococcus aureus from Gram-positive bacteria and Escherichia coli (AUGMKK) from Gram-negative bacteria were used to test the antibacterial activity of black mulberry juice samples. In the second part of study, it was aimed to determine antifungal and antibacterial activity of black mulberry juice during heating at 70 degrees C for 9 h, 80 degrees C for 7.5 h and 90 degrees C for 5 h. While the zone diameter of untreated black mulberry juice against S. aereus was determined as 12.68 +/- 0.69 mm, it was determined as 13.92 +/- 1.11 mm for clarified black mulberry juice. The antibacterial effect was increased by Pasteurization in untreated fruit juice against Staphylococcus aereus (13.67 +/- 0.41 mm), while it was found to be slightly lower in clarified fruit juice (12.78 +/- 1.00 mm). Only untreated black mulberry juice samples had antibacterial activity against Escherichia coli ((12.32 +/- 0.67 mm). Besides, it was not determined antifungal activity against all microfungi during clarifying and heating. According to the variance analysis data, clarification and pasteurization processes were effective on titration acidity and only pasteurization process had effect on pH (P<0.01).