Collisional quantum interference (CQI) on rotational energy transfer was observed in Na-2 (A(1) Sigma(u)(+) , upsilon = 8 similar to b(3)Pi(0u), upsilon = 14) system in collision with Na, but the interference angle was not measured out due to the lack of enough experimental data. As a complementarity of the experiment, the interference angle is calculated theoretically in this Letter, based on the time-dependent first order Born approximation, and taking into account the anisotropic Lernnard-Jones interaction potentials. The calculated value gives a quantitative and accurate description of CQI. (C) 2004 Elsevier B.V. All rights reserved.