The growth of underdoped Bi2Sr2CaCu2O8+delta (Bi-2212) single crystals has been Studied by the traveling solvcnt floating zone (TSFZ) technique under low oxygen pressures p(O-2) 1, 8 x 10(-1), 5 x 10(-1), 1 x 10(-1), 5 x 10(-2), 1 x 10(-3) and 5 X 10(-4) bar, respectively. A starting composition of Bi2.1Sr1.9CaCu2O8+delta and a slow growth rate of 0.2 mm/h were employed for the growth. The effect of oxygen pressure on the growth habit, structure and superconducting properties of underdoped Bi-2212 crystals was investigated. It was observed that the stability of the molten zone and the size of crystals were not sensitively influenced by decreasing p(O-2) from 1 to 5 x 10(-4) bar. however. the oxygen distribution in Lis-grown crystals became inhomogeneous as p(O-2) decreased. Underdoped Bi-2212 crystals with the considerable size up to 15 x 5 x 1 mm(3) were obtained. X-ray diffraction (XRD) Studies indicate that the as-grown crystals have orthorhombic symmetry. The crystals do not show phase decomposition until growth pressure p(O-2) 1 x 10(-3) bar and the Bi-2212 phase decomposes significantly when p(O-2) decreased to 5 x 10(-4) bar, according to XRD results. With decreasing p(O-2) from 1 down to 1 x 10(-3) bar the c-axis extends monotonically from 30.731(0) to 30.912(8) Angstrom while the Superconducting transition temperature T, reduces from 92 to 79 K and the transition width, AT, increases from 2 to 10 K. A further decrease of p(O-2) to 5 x 10(-4) bar leads to a broader DeltaT(c) (similar to20 K) due to the oxygen inhomogeneity and phase segregation. (C) 2002 Elsevier Science B.V. All rights reserved.