Solution:
Two to one.  

Explanation:
Draw the smaller square's diagonal to see that the the smaller square's diagonal is the diameter of the circle. Divide the larger square into two equal rectangular halves to see that the larger square's side is also the diameter of the circle. This means that the smaller square's diagonal equals the larger square's side. (Or, if you prefer, simply rotate the inner square by 45 degrees.) As we've seen in the earlier puzzle "The Unkindest Cut Of All," the area of the smaller square is half that of the larger, making the ratio two to one.