Cut the radish into small cubes (about 2.5 cm / 1 inch) and put them into a sterilized glass jar.
Combine water, sugar, vinegar and salt in a sauce pan and bring them to boil over low to medium low heat until the sugar dissolves (about 2-3 mins). Stir often.
Pour the brine over the radish and close the lid. Leave at room temperature for 3-4 hours then refrigerate. It should be ready to eat in 1 – 2 days.
Serve with your favorite main meal. (e.g. Korean fried chicken). It can be refrigerated in an air tight container for a few weeks.
