A search for neutron-antineutron ($n-\bar{n}$) oscillation was undertaken in<br />
Super-Kamiokande using the 1489 live-day or $2.45 \times 10^{34}$ neutron-year<br />
exposure data. This process violates both baryon and baryon minus lepton<br />
numbers by an absolute value of two units and is predicted by a large class of<br />
hypothetical models where the seesaw mechanism is incorporated to explain the<br />
observed tiny neutrino masses and the matter-antimatter asymmetry in the<br />
Universe. No evidence for $n-\bar{n}$ oscillation was found, the lower limit of<br />
the lifetime for neutrons bound in ${}^{16}$O, in an analysis that included all<br />
of the significant sources of experimental uncertainties, was determined to be<br />
$1.9 \times 10^{32}$~years at the 90\% confidence level. The corresponding<br />
lower limit for the oscillation time of free neutrons was calculated to be $2.7<br />
\times 10^8$~s using a theoretical value of the nuclear suppression factor of<br />
$0.517 \times 10^{23}$~s$^{-1}$ and its uncertainty.