  We present a detailed study of the collider observable $m_{T2}$ applied for
pair-produced superparticles decaying to visible particles and a pair of
invisible lightest supersymmetric particles (LSPs). Analytic expressions of the
maximum of $m_{T2}$ over all events ($m_{T2}^{\rm max}$) are derived. It is
noticed that if the decay product of each superparticle involves more than one
visible particles, $m_{T2}^{\rm max}$ being a function of the {\it trial} LSP
mass ${m}_\chi$ has a kink structure at ${m}_\chi=$ true LSP mass, which can be
used to determine the mother superparticle mass and the LSP mass
simultaneously. To see how well $m_{T2}^{\rm max}$ can be constructed from
collider data, a Monte-Carlo analysis of the gluino $m_{T2}$ is performed for
some superparticle spectra.
