For the understanding of the mechanism of high-Tc suuperconductivity, (i). We determined the band structure of single crystal of Bi2Sr2CaCu2O8 by angle-resolved resonant photoemission experiment. Two dispersive bands with mainly oxygen 2p character were observed in the vicinity of the Fermi level and one of them crosses the Fermi level. This result shows the direct evidence of the Fermi-liquid states with oxygen 2p character. (ii). We performed NMR study of enriched 17 O in the CuO2 plane of the superconducting Y-Ba-Cu-O system. We found BCS-like enhancement of 17 O nuclear spin-lattice, relaxation rate 1/T1 below Tc. This shows an evidence that the high-Tc superconductivity is of s-wave type with oxygen p-hole Cooper pairing. (iii). We observed an oxygen isotope shift in Bi-Sr-Ca-Cu-O superconductors when 18 O is substituted for 16 O . The superconducting transition temperature Tc is lowered by about 0.32 K for the higher-Tc phase (Tc = 110K) and by about 0.34 K for the lower-Tc phase (Tc = 75K). These results show the evidence of a measurable contribution to the superconductivity from phonons.