Sterilize a one quart jar and add blueberries to the jar.
Bring the vinegar and sugar just to a boil, stirring to dissolve the sugar, and then pour over the berries. Top the jar with wax paper or parchment paper to keep the lid from corroding. Screw on the lid and shake the jar. Place it in a cool, dark place for about a week, shaking it daily. Strain out the solids and pour the vinegar back into a sterilized jar. Keeps at room temperature for 3 months, refrigerated for 6.