My boss has 2 IRAs. He is taking RMDs from each. He wants to know if he can combine them and take one RMD from the combined IRA.

One of the IRAs has the following history: Boss had a Keogh Plan with a single member. He was told he had to terminate it and put it in an IRA which he did.

Is there any reason he can't combine the two IRAs?

As long as all of the money in both IRAs is pre-tax, and it probably is, there's no reason you can't combine them. It used to be that you might want to keep a rollover IRA (the second one that came from the Keogh) separate in case you wanted to roll it back into a qualified plan, but you can roll any IRA money into most plans so that's not a factor.

He can combine... but one reason for not combining could also be FDIC insurance coverage limit at the single financial institution (this assumes that the IRA funds are invested in Cash or Cash Equivalents)