The objective of the research study was to determine the effect of time and temperature of storage on the stability of folic acid and folates in fortified fruit and fruit-vegetable juices. The contents of folic acid and folates were determined in fresh juices and in juices stored for 3, 6, and 9 months at temperatures ranging between 20 and 22 °C and in juices stored in a refrigerator (5 to 7 °C). No significant losses of folic acid were reported in any of the analyzed juices that were stored for 3 months, irrespective of the storage temperature. The highest losses were reported in the juices having the lowest pH of 3.45 (clarified fruit juice) and 4.25 (fruit-vegetable puree type of juice) and stored for 9 months. In the juice samples analyzed, very low amounts of only one identified natural form of folates were determined, i.e. of 5-methyltetrahydrofolate (5CH₃FH₄). No significant losses of 5-methyltetrahydrofolate were found to occur in juices stored not longer than for 3 months at temperatures ranging from 20 to 22 °C; however, in the juices stored for 9 months, there were reported losses of this vitamin, especially in the juices stored at a room temperature.