  We search for optical transient sources with durations of $\sim 0.1$ to $\sim
1.3$ s using a dataset obtained in the Organized Autotelescopes for
Serendipitous Event Survey (OASES) observation campaign. Since the OASES
observations were carried out using two independent wide-field and high-cadence
observation systems monitored the same field simultaneously, the obtained
dataset provides a unique opportunity to develop a robust detection method for
sub-second optical transients. In the dataset of a selected field around the
ecliptic and the Galactic plane, we find no astronomical event candidate that
satisfies our detection criteria. From the non-detection result, we derive an
upper limit on the event rate of sub-second transients around the ecliptic and
the Galactic plane for the first time, obtaining $\sim 0.090$ and $\sim
0.38~{\rm hr^{-1}~deg^{-2}}$ for $m = 12$ and 13 Vmag, respectively. In
addition, future prospects of the sub-second scale transient event surveys are
discussed.
