Manipulation of microscale particles and fluid liquid droplets is an important task for lab-on-a-chip devices for numerous biological researches and applications, such as cell detection and tissue engineering. Particle manipulation techniques based on surface acoustic waves (SAW) appear effective for lab-on-a-chip devices because they are non-invasive, compatible with soft lithography micromachining, have high energy density, and can work for nearly any type of microscale particles. In this thesis, a new two-stage particle separation device based on standing surface acoustic waves was developed. The different sizes of particles were firstly focused in a line at the first stage and then separated at the second stage. This device only utilizes standing surface acoustic force in both stages, does not require sheath flow, avoiding any risk of contamination of sample and simplifying the stature of the device.The electrode was patterned and etched on a golden coated LiNbO3 wafer by photolithography. The PDMS microchannel was fabricated by curing it on a mold that was fabricated on glass substrate also by photolithography. Then we bonded the electrode and PDMS channel together under a microscope with designed align marks. The device was tested using two kinds of micro particles with different sizes, 20 ¿¿¿¿m polystyrene beads and 5 ¿¿¿¿m polystyrene beads, which were separated in a short time. Experimental conditions including applied voltage, frequency and flow velocity were optimized to increase efficiency and throughput. A high throughput of 50 ¿¿¿¿L/hour was achieved by this device, which is a few time higher than that of existing similar micro devices (typically have a throughput less than 20 ¿¿¿¿L/hour). A SSAW separation device with a wide separation channel was also tested to increase the throughput dramatically. The throughput of this wide channel device can reach up to 300 ¿¿¿¿L/hour. The feasibility of separating blood was studied and confirmed by calculation as well.