We calculate the contribution to the B\to \pi \pi decay from gluonic penguin operator, O_8g, including both hard O(\alpha _s) and soft gluon effects. As expected, the soft effects enter at order 1/m_b², but are numerically of the same order as the hard ones, indicating the necessity of taking them into account.

PACS numbers: 12.38.Lg, 11.55.Hx, 13.25.Hw