Put the sour cherries into a 1-quart Mason jar, and cover with the sugar. Seal the jar and shake it several times until the cherries are well coated with sugar. Add the vodka, reseal and shake the jar a few more times to mix.
Set aside in a cool, dark place for 4 weeks. Strain the mixture through a fine sieve into a large glass measuring cup or glass bowl. Transfer the liqueur to a nice bottle. The Sour Cherry Vodka is ready to drink immediately after the 4 weeks fermenting and has a shelf life of 2 to 3 months.