The lender is increasing the total number of buy-to-let properties it will allow a landlord customer to own from four to 10.
This total will include unencumbered properties and properties mortgaged with NatWest and another lender.
The move will bring it into the Prudential Regulation Authority’s (PRA) portfolio lending guidelines.
NatWest’s current £50,000 minimum income for aggregated borrowing over £1m will be removed.
However, all customers will be required to meet a standard buy-to-let (BTL) minimum income of £25,000.
NatWest is also increasing its maximum aggregate customer borrowing allowed to £3.5m, up from £2m.
NatWest Intermediary Solutions service development manager Sarah Taylor said: “This important step will simplify our BTL policies and means we can be there for a wider customer range in what is a growing market.”