Biosensors are widely used in many fields, such as environmental detection, food analysis, military and medicine. Because of their high sensitivity and low noise, optical biosensors attract the most attention. As one kind of optical biosensors, liquid core optical ring resonator (LCORR) is small in size and has high Q-factor (up to 109), which has the potential to become a promising technology platform for future sensitive, miniaturized and lab-on-a-chip type sensors. The devices are investigated theoretically and experimentally in details. Ultra-thin micro-capillaries are fabricated by an improved technique which combines the outer etching and the stretching of the heated LCORR to accurately control the stretching velocity. The Q-factor and the sensitivity of LCORR are tested by injecting pure water, acetone, or NaCl solution of different concentrations into them. The LCORR show high sensitivity of about 61.5 nm/RIU and have great stability.