"J'aime ma mère."
Here's a breakdown:
* J'aime: I love
* ma: my
* mère: mother/mum
You can also be more affectionate and say:
* "Je t'aime, Maman." (I love you, Mum)
* "Je t'aime beaucoup, Maman." (I love you very much, Mum)
* "J'adore ma mère." (I adore my mother)
Remember: French is a gendered language, so you'll need to use "mère" (feminine) for your mother.