The thermal behavior and crystal transformation precesses from I to II and from II to I for (Et4NBH4)-B-10 and from I' to II' and from II' to I' for (Et4N)(2)B20H18 are determined by DSC. The results show that their crystal transformation processes are reversible. The values of Delta H-cr and Delta S-cr are 101.0 J g(-1) and 38.68 J mol(-1) k(-1) for (Et4NBH4)-B-10 and 148.4 J g(-1) and 182.7 J mol(-1) k(-1) for (Et4N)(2)B20H18, respectively. The apparent activation energy (E) and pre-exponential constant (A) are 213.0 kJ mol(-1) and 10(17.7) s(-1) for (Et4NBH4)-B-10, and E-1=105.4 kJ mol(-1), A(1)=10(9.1) s(-1), E-2=180.2 kJ mol(-1), A(2)=10(15) s(-1) for two exothermic processes of (Et4N)(2)B20H18, respectively.