Mix Jell-O according to packet instructions, in bowl, except omit one cup of water for liquid from can of mandarin oranges.
Using electric hand mixer beat Jell-O mixture with cream cheese until few lumps are present. Next using electric mixer beat in Cool Whip until thoroughly mixed. Using spoon, mix in mandarin oranges and pineapples.
Pour mixture into Jell-O mold and top with marshmallows. Place mold in refrigerator, until set.