In most cases, probably not. 401K’s are not liquid in that you typically cannot access them without leaving your employer. Even if a lender were to allow you to use them as reserves, you typically have to document the circumstances under which you can make withdrawals. They just are not liquid enough compared with money markets, savings, and non-retirement accounts. The purpose of requiring a borrower to have reserves is to insure that if a cash crunch arises, there will still be funds available to make the mortgage payment. If you have to tap a 401K to do that, it could be a lengthy process to get a loan or make a withdrawal.