The objective development of laser-Doppler Velocimetry (LDV) technique for fluid investigation is to produce a tool, which provides non-invasive and instantaneous measurements for velocity points in difficult situations such as in small ducts or channels. A single velocity component measurement based on fiber-optic probe is carried out using Helium-Neon Laser as the light source. The work includes the design and construction of the test-flow rig, the auxillary tools and accessories for LDV research facilities. As an alternative to the use of costly signal processing hardwares which are produced commercially, data analysis is based on available systems. In this study, fast Fouries Transform method is used for extracting the Doppler frequency which is proportional to the velocity of the particles in water. The results of the investigation indicate that the LDV system is linear and the flow-test facilities provide reliable data for laminar flow in straight pipes or ducts (square pipe 20 X 20 mm) over a wide range of Reynolds number. The distribution of the axial velocity is in the range of 1.2 cm/s to 13 cm/s which corresponds to measured Doppler frequency of 2-25 kHz. LDV experiment has also been carried out on simple two-phase flows (i.e aerosol spray of water from nebulisher). This results in higher amplitudes for the frequencies, mean velocities,velocities and greater spread in dispersion (the probability distribution) compared to a single phase flow. For water flowing in the square duct, the experimental results are in good agreement with the computational data whereby the intensity of turbulence is about 3 & at the centreline and slightly higher than 7 & towards the solid wall. The validity of the results is confirmed by comparing the results with that of other workers. Conventional method of flowrates measurement and flow visualisation techniques were also carried out. A validation scheme was adopted for acquiring the mean Doppler frequencies and results of mean velocities were compared by using a computational modelling technique. An investigation was also carried out for water flows in small channels (20 X 10 mm) with structure configuration of sudden change in cross-sectional area of the flow line. The experiment was performed to prove the sensitivity of the techniques. These small scale studies are prerequisites for the future modelling of flow structures and flow of incompressible fluids (e.g the flow of blood in artery). The present study also indicates that the use of digital oscilloscone and transient recorders interfaced to a personal computer can provide a suitable solution to signal processing and data acquisition problems in LDV technique.