  We present new observations with the Atacama Large Millimeter/submillimeter
Array for a gravitationally-lensed galaxy at $z=9.1$, MACS1149-JD1. [O III]
88-$\mu$m emission is detected at 10$\sigma$ with a spatial resolution of
$\sim0.3$ kpc in the source plane, enabling the most distant morpho-kinematic
study of a galaxy. The [O III] emission is distributed smoothly without any
resolved clumps and shows a clear velocity gradient with $\Delta V_{\rm
obs}/2\sigma_{\rm tot}=0.84\pm0.23$, where $\Delta V_{\rm obs}$ is the observed
maximum velocity difference and $\sigma_{\rm tot}$ is the velocity dispersion
measured in the spatially-integrated line profile, suggesting a rotating
system. Assuming a geometrically thin self-gravitating rotation disk model, we
obtain $V_{\rm rot}/\sigma_V=0.67_{-0.26}^{+0.73}$, where $V_{\rm rot}$ and
$\sigma_V$ are the rotation velocity and velocity dispersion, respectively,
still consistent with rotation. The resulting disk mass of
$0.65_{-0.40}^{+1.37}\times10^{9}$ M$_\odot$ is consistent with being
associated with the stellar mass identified with a 300 Myr-old stellar
population independently indicated by a Balmer break in the spectral energy
distribution. We conclude that the most of the dynamical mass is associated
with the previously-identified mature stellar population that formed at
$z\sim15$.
