Legal Question in Landlord & Tenant Law in California

If you mean while your lease is in effect can your landlord legally rent the space to someone else, clearly not as that is a breach of the lease. If, however, you have breached the lease and given up possession before the lease would expire had you not breached it, then the landlord has a duty to try to re-rent the place as soon as is reasonably possible in order to reduce the damages you are responsible for [mitigation of damages].