What to say in PhD application when potential advisor is moving to another university? I am in the process of applying to PhD programs in Computer Science. A professor with whom I'm interested in working is moving from university A to university B. While he is not super well-known, his research interests and mine align very well, and I am quite sure I would have been admitted to university A had he remained there.

He will not moving to B until latter half of 2015, which means that he will not be able to give input into PhD applications to university B for the 2015 admissions cycle.

I will be applying to university B (with the hope that I can work with him), but is there anything that I can (or should) do with regard to my application? Or just mention it in SoP?

(B is slightly more competitive than A, and both are top 15 schools)
which means that he will not be able to give input into PhD applications to university B


This is incorrect. He certainly can, if he chooses, e-mail the director of graduate admissions at B, say that he's interested in working with you, and ask him/her to consider your application favorably. They don't have to admit you, but that would be true even if he were at B now and had been there a long time.

I'd recommend mentioning this in your SOP, and perhaps also e-mailing him and letting him know that you are applying to B with the idea of working with him. (If you have not done so already.)

That said, "I am quite sure I would have been admitted to university A had he remained there" sounds possibly a bit presumptuous, although I don't know your circumstances. In any case, do what you would have done if this professor wasn't moving: apply to the graduate program where he'll be, let him know, and hope for the best. Good luck.