In a medium saucepan, combine sugar, water, rhubarb and strawberries. Stir well.
Bring the mixture to a boil over medium-high heat, stirring occasionally.
Once boiling, remove the pan from heat and cover.
Let steep for approximately 30 minutes.
Drain the simple syrup into an airtight container.
Let cool in the refrigerator.
Store in the refrigerator and use as desired. The syrup will last up to several weeks.