The anisotropy of low-temperature thermal expansion of the high-temperature superconductor Bi2Sr2CaCu2O8(Bi-2:2:1:2) is analyzed theoretically. The generalized Grüneisen parameters (GPs) of elastic waves propagating in different directions of Bi-2:2:1:2 are calculated using the measured values of second order elastic constants and first order pressure derivatives of second order elastic constants. For this, we have used the measured values of the second order elastic constants of G. A. Saunderset al. The 12 third order elastic constants of the Bi-2:2:1:2 system are calculated from the expressions of effective second order elastic constants. All the third order elastic constants are negative exceptC155andC112. Some values of generalized Grüneisen parameters are negative. The generalized GPs γ″jare all positive except γ″2(−0.048) at θ = 85°. The Brugger gammas are calculated and the low-temperature limits of the Grüneisen gamma are determined using the procedure of Menon and Ramji Rao. γ−Lhas the value of 4.4 for the Bi-2:2:1:2 system. The low-temperature limit of the Grüneisen gamma is positive. Therefore, we expect volume expansion to be positive down to absolute zero for the Bi-2:2:1:2 system. The anisotropy of thermal expansion along thecaxis of the compound is very much higher than that along other directions.