  We discuss some properties of an M-9-brane in ``massive 11D theory'' proposed
by Bergshoeff, Lozano and Ortin. A 10-form gauge potential is consistently
introduced into the massive 11D supergravity, and an M-9-brane Wess-Zumino
action is constructed as that of a gauged $\sigma$-model. Using duality
relations is crucial in deriving the action, which we learn from the study of a
9-form potential in 10D massive IIA theory. A target space solution of an
M-9-brane with a non-vanishing 10-form gauge field is also obtained, whose
source is shown to be the M-9-brane effective action.
