Hi guys, I bought a California Oak about a week ago but a few days ago I just realizes that there is something wrong with the leves.
Any one knows what is it and how to solve it?

Without a picture and some information about placement etc we can’t tell anything

I uploaded the picture. Where is it? Actually I saw it in the preview.
Let me try again.

California oak is a decious tree and should not have leafs in most of the world right now. In northern hemisphere some oaks may have sprung into leaf, but not that mature as I can see on your picture. In southern hemisphere they are about to fall now so no issue then.

So... are you in the northern of southern hemi?
Is the plant outside or inside....

I'm in North California and the tree is outside.

So you should be able to go out and check what the status is for wild specimens and compare with your tree.

It looks like your tree still has last years leafs on. They need to drop so new ones can grow. Unsightly old leafs is no problems. But old leaves still on the tree in spring might indicate that it hasent went true a natural dormancy period.

Wikipedia says California oak is evergreen.

I googled it and found recources saying decidious.

Now on a second attempt i found this page which look trustworthy:

nature.berkeley.edu/garbelottowp/?p=1749

All native californian oaks but none of them called californian oak. I guess the same issue as allways, better using the scientific name to be sure what species we are talking about.