The super low thermal conductivity and ultrahigh thermal expansion of Ba(6)Ln(2)Al(4)O(15) (Ln = Gd, Dy, Er, and Yb) compounds with one-sixth of the oxygen vacancy have been synthesized by the solid-state reaction method. The lowest thermal conductivity of Ba6Yb2Al4O15 was found to be 0.98W/(m.K) at 1073K. The large concentration of oxygen vacancies in Ba(6)Ln(2)Al(4)O(15) compounds leads to low elastic modulus and loose chemical bonds. The average thermal expansion coefficients of Ba(6)Ln(2)Al(4)O(15) compounds was 11.8x10(-6) 13.6x10(-6) K-1. The loose chemical bonds with Young's moduli were in the range of 102.8 135.9 GPa.