Crush apples and pears in a large saucepan and stir in cinnamon.
Thoroughly mix sugar and lemon juice with fruits and bring to a boil over high heat, stirring constantly.
Immediately stir in pectin. Bring to a full rolling boil and boil hard 1 minute, stirring constantly.
Remove from heat, quickly skim off foam, and fill hot, sterile jars leaving 1/4-inch headspace. Adjust lids and process in a boiling water bath for 5 minutes.
To sterilize empty jars, place them right side up on the rack in a boiling-water canner. Fill canner and jars with hot (not boiling) water to 1 inch above jar tops. Boil 10 minutes below 1,000 feet elevation, adding 1 minute for each additional 1,000 feet. Remove and drain hot sterilized jars one at a time as filled.