I just realized that my husbands 401k is not in an fdic insured institution. Can a 401k be rolled over into another 401k in an institution that is insured?

You are stuck with whatever institution your employer has selected to administer your 401(k), and the investements in the plan. So no, you cannot move it to an institution of your choice. However, if you are no longer with the company where the 401(k) is located, you can move your 401(k) balance to a rollover IRA, and then you have lots of choices. Remember that FDIC insurance applies only to cash deposits in individual or joint bank accounts, so you would have to roll the account to an IRA at a bank and put it into a cash account. Alternatively, you are protected by SIPC for accounts at traditional brokerage houses. Both FDIC and SIPC protect you against losing your cash if the institution goes bust, but they do not protect your investment from loss of value (except for cash deposits). Here's some helpful information:

Are Your Retirement Accounts Safe?

Its highly unlikley that 401K assets are invested in an FDIC institution. His 401K assets are invested in investment grade vehicles, not cash savings accounts.

If you are concerned about the solvency of the administrator of the plan contact the company about switching.

But I believe 401Ks are covered by the PBGC a similar account guarantor.

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SusanYeattsCFP disagrees: 401ks are not guaranteed by PBGC. Solvency of the investment firms is most likely SIPC covered,but 401k plans are not pension plans and do not qualify for PBGC coverage.

Thanks for the clarification. You are correct that the PBGC only covers defined benefit plans.

401Ks are defined benefit plans that come under the unbrella of retirements plans covered by ERISA which also setup the PBGC. Hence my confusion.