In the title salt, K(+)·C(4)H(7)BF(3)O(-), the K atom is surrounded by six anions making close contacts through seven F [K⋯F = 2.779 (1)-3.048 (1) Å] and two O [K⋯O = 2.953 (2) and 3.127 (2) Å] atoms in a trivacant fac-vIC-9 icosa-hedral coordination geometry.