Abstract: The main chemical composition of ruby is Al₂O₃,and with the trace elements of Fe,Cr,Ti,Mn,Si,Mg,Ca,Na, K and so on.The different contents of the trace elements result in the differences in the colours of rubies.In order to research the causes of colour of ruby from Ailao Mountain,Yunnan Province,8 pieces of ruby rough samples with different colours collected are tested by means of ultraviolet-visible spectrophotometer,electron microprobe and inductively coupled plasma mass spectrometry(ICP-MS).The trace elements and chemical compositions of the samples are studied.The characteristics of trace elements of rubies from four localities——Mong Hsu of Burma,Thailand,Yunnan Provice of China,and Yen Bai of Vietnam——are analysed and discussed.The chemical composition characteristics of the ruby samples from Ailao Mountain,Yunnan Province,are summarized.The rubies from Yunnan Province are rich in Cr and poor in Fe,and the content of Cr results in the changes of the shades of red hue directly.