  We calculate the branching ratio of $\Lambda_b \to \Lambda \gamma$ in the
standard model using the PQCD method. The predicted branching ratio
$B(\Lambda_b \to \Lambda \gamma)$ is about $(4.3\sim 8.6)\times 10^{-8}$, with
reasonable parameter ranges in the heavy baryon distribution amplitude. This
branching ratio is much smaller than those obtained in other hadronic model
calculations. Future experimental data can provide important information on
applicability of the PQCD method to heavy baryon radiative decay.
