The PHENIX experiment at RHIC has measured $\omega$, $\eta$ and $K^{0}_{s}$ mesons through the multi-particle hadron decay modes in $p+p$, $d+Au$ and $Au+Au$ collisions at $\sqrt{s_{NN}}=200 GeV$. We will present $\omega$-meson data at $\sqrt{s_{NN}}=200 GeV$ from $p+p$ and $d+Au$ collisions in the $p_{T}$ range from 2.5~$GeV/c$ to 9~$GeV/c$, and the first results from $Au+Au$ $\sqrt{s_{NN}}=200 GeV$. The $\omega$ carries unique information about medium modification effects. A large fraction of $\omega$-mesons decay when the energy density of the system is above the threshold of the phase transition from Hadronic Matter to QGP. Changes in the property of the medium could be reflected in the modification of the yield and mass of the $\omega$. Comparison of the $\omega$ yield and width in the hadron and di-lepton channels could provide significant evidence of a new state of matter, and help to study its properties. These hadron decay results set the baseline for such a comparison.