  Speckle interferometric observations made with the 6 m telescope of the
Special Astrophysical Observatory of the Russian Academy of Sciences in 2000
revealed the triple nature of the nearby ($\pi_{Hip}=51.80\pm1.74$ mas)
low-mass young ($\approx200$ Myr) star GJ 900. The configuration of the triple
system allowed it to be dynamically unstable. Differential photometry performed
from 2000 through 2004 yielded $I$- and $K$-band absolute magnitudes and
spectral types for the components to be $I_{A}$=6.66$\pm$0.08,
$I_{B}$=9.15$\pm$0.11, $I_{C}$=10.08$\pm$0.26, $K_{A}$=4.84$\pm$0.08,
$K_{B}$=6.76$\pm$0.20, $K_{C}$=7.39$\pm$0.31, $Sp_{A}$$\approx$K5--K7,
$Sp_{B}$$\approx$M3--M4, $Sp_{C}$$\approx$M5--M6. The ``mass--luminosity''
relation is used to estimate the individual masses of the components:
$\mathcal{M}_{A}$$\approx0.64\mathcal{M}_{\odot}$,
$\mathcal{M}_{B}$$\approx0.21\mathcal{M}_{\odot}$,
$\mathcal{M}_{C}$$\approx0.13\mathcal{M}_{\odot}$. From the observations of the
components relative motion in the period 2000--2006, we conclude that GJ 900 is
a hierarchical triple star with the possible orbital periods
P$_{A-BC}$$\approx$80 yrs and P$_{BC}$$\approx$20 yrs. An analysis of the 2MASS
images of the region around GJ 900 leads us to suggest that the system can
include other very-low-mass components.
