Pare and core the pineapple, then chop fine.
Combine the pineapple, sugar, 1 cup water and the lemon slices in a Dutch oven and place over low heat.
Bring to a boil, stirring until the sugar dissolves.
Boil over high heat, stirring frequently for about 30 minutes or until the jam sheets from a spoon.
Pour immediately into hot sterilized jars and seal.