The Schwinger-boson mean-field theory is applied to the quantum ferrimagnet
ic Heisenberg chain. There is a ferrimagnetic long-range order in the groun
d state. We observe two branches of the low-lying excitation and calculate
the spin reduction, the gap of the antiferromagnetic branch, and the spin f
luctuation at T=0 K. These results agree with the established numerical res
ults quite well. At finite temperatures, the long-range order is destroyed
because of the disappearance of the Bose condensation. The thermodynamic ob
servables, such as the free energy, magnetic susceptibility, specific heat,
and the spin correlation at T>0 K, are calculated. The T chi(uni) has a mi
nimum at intermediate temperatures and the spin-correlation length behaves
as T-1 at low temperatures. These qualitatively agree with the numerical re
sults and the difference is small at low temperatures. [S0163-1829(99)07225
-2].