Lingonberry is a popular fruit in the Nordic countries, where many variations of lingonberryproducts are available. The berry naturally contains high amounts of antioxidants andantimicrobial substances which make it an ideal natural preservative. The jui ce of lingonberryis also naturally low in pH which is often perceived as too sour in taste. To better utiliselingonberry juices as themselves or in combination with other ingredients, transformation ofthe juices is required to improve the palatability. The current study explored the possibility ofconverting malic to lactic acid using lactic acid bacteria, determine the changes in sensorycharacteristics of the fermented juices as well as blends thereof with blackcurrant juice, andinvestigate the microb ial stability of the juices when challenge tested. Lingonberries werepressed and the juices were fermented with L. plantarum. In order for the fermentation to beunimpeded due to active benzoic acid and successfully complete the conversion from malicacid to lactic acid, the pH of lingonberry juice was increased from 3.0 to 5.2. The resulting pHafter fermentation had stabilised to 4.9 after 7 days.To prepare the fermented lingonberry juices in a context of a mixture of juices, fermentedjuices were pasteurised and prepared in blends with diluted blackcurrant juice (25%) in fivedifferent proportions of lingonberry/blackcurrant juice; 0/100, 25/75, 5 0/50, 75/25, and 100/0.These five juices were evaluated with a sensory panel using descriptive analysis, along with anon fermented lingonberry juice. The juices evaluated showed that fermentation significantlyp <0.001) reduced the perceived sourness and astringency, seen from the difference betweenfermented and non fermented lingonberry juices. The fermentation had also significantlyp <0.001) increased the perceived sweetness of the juices.The five blends were also subjected to challenge tests using three microbial speciescommonly found in juices. In none of the samples the bacterium Listeria monocytogenes wereable to grow likely due to the low pH (3.07 4.98) possibly in combination with benzoic acid.The yeast, Candida albicans were only able to grow in 0/100 lingonberry/blackcurrant juice,which did not contain any benzoic acid. When testing Aspergillus brasiliensis, full growthcould only be observed in 0/100 lingonberry/blackcurrant j uice. In the blends, mould growthswere delayed in a concentration dependent manner where no growth was observed in the 100% fermented lingonberry juice even after six weeks. The challenge test overall indicated thatblends containing lingonberry juice pr event fungal growth although a high concentrationmight be required to prevent mold growth.