Water? Assuming there's no other signs of disease such as infestation, brown spots on the leaves, scale on the trunk, etc.

Watering twice a day, thank you anyway for an answer.

Only other thing I can think of is hot sun - this plant likes cool shade.

Really.....and Iv been told Magnolia doesnt like only early sunlight, maybe could be a reason.Thank you again.

Magnolia grandiflora will tolerate a little sun, but the vast majority of them prefer shady conditions.