The structure, thermal stability and elasticity of Zr50Cu40Al10 bulk metallic glass (BMG) have been investigated with reference to Zr70Cu30 and Zr70Cu20Al10 amorphous alloys. The thermal stability of Zr50Cu40Al10 is significantly enhanced in comparison compared with those of the others. The large total coordination numbers more than 11 around all constituent elements are observed in Zr50Cu40Al10. A change of the bulk modulus in the crystallization is extremely small in Zr50Cu40Al10. The present experimental results indicate that atoms in the Zr50Cu40Al10 glass are closely packed and its microstructure is fairly uniform. This results in the much higher thermal stability of Zr50Cu40Al10.