Cherish: to love sb/sth very much and want to protect them or it Treasure: to have or keep sth that you love and that is extremely valuable to you => these words are synonyms

Cherish: 1. To treat with affection and tenderness; hold dear: cherish one's family; fine rugs that are cherished by their owners. 2. To keep fondly in mind; entertain: cherish a memory. Synonyms : to appreciate. To treasure: to keep and care for something that is very special, important, or valuable to you: Jim treasured the gold pocket watch that his grandfather had given him. Read more: http://www.answers.com/

As verbs, they mean the same thing and can be used interchangeably. But in some phrases, a native speaker may prefer to use one more than the other. "I will cherish this moment forever. "I will treasure this moment forever." Here is a great song using the word "cherish": http://www.youtube.com/watch?v=AH7zq82UzIg