Combine raspberries and sugar in a medium saucepan; slowly bring to a boil, stirring frequently. Boil, stirring occasionally, 8 to 10 minutes or until mixture thickens. Remove from heat, and skim off foam with a metal spoon.
Quickly ladle preserves into hot sterilized jars, leaving 1/4- inch headspace. Cover at once with metal lids, and screw bands tight. Process preserves in boiling-water bath 15 minutes.