  Young exoplanets are attractive targets for atmospheric characterization to
explore the early phase of planetary evolution and the surrounding environment.
Recent observations of the 10 Myr young Neptune-sized exoplanet K2-33b revealed
that the planet's transit depth drastically decreases from the optical to
near-infrared wavelengths. Thao et al. (2022) suggested that a thick planetary
haze and/or stellar spots may be the cause; however, even the best-fit model
only barely explains the data. Here, we propose that the peculiar transmission
spectrum may indicate that K2-33b possess a circumplanetary dust ring, an
analog of Jupiter's dust ring. We demonstrate that the ring could produce a
steep slope in the transmission spectrum even if its optical depth is as low as
$\sim {10}^{-2}$. We then apply a novel joint atmosphere-ring retrieval to
K2-33b and find that the ring scenario could well explain the observed spectrum
for various possible ring compositions. Importantly, the dust ring also
exhibits prominent absorption features of ring particles around $\sim$10
$\rm{\mu}m$, whose shape and strength depend on the composition of the ring.
Thus, future observations by JWST-MIRI would be able to test not only the ring
hypothesis but also, if it indeed exists, to constrain the composition of the
ring -- providing a unique opportunity to explore the origins of the dust ring
around its parent planet, soon after the planetary system's formation.
