Under Article 7 of Qatar's Property Leasing Law (Law No. 4 of 2008), your landlord cannot charge you a security deposit of more than two months' rent for residential properties. This cap is a legal protection for tenants, so any demand exceeding this amount for a residential lease is not permitted.
For non-residential premises (such as commercial or industrial units), the law allows the landlord and tenant to agree on a different deposit amount, so the two-month limit does not apply in those cases.
Practical tip: Always get a written receipt for your security deposit and keep a copy of your signed lease agreement. If your landlord attempts to charge more than two months' rent as a deposit on a residential property, you can refer the matter to the Real Estate Lease Registration Office established under Article 20 of the same law.
This is general legal information, not legal advice. For advice on your specific situation, consult a lawyer licensed in Qatar.