We have developed a compact, high-performance turbidimeter that provides highly sensitive measurement with a reduced cell length by solving problems with conventional models. To achieve good linearity in wide measuring ranges, the optical system (hardware) and the signal processing (software) had been examined. The new turbidimeter utilized the characteristics of the method that measures the ratio of scattered to transmitted light same as the previous model. To improve the linearity, however, some amounts of scattered light current were added to the transmitted light current. In conjunction with this, software process was implemented. In addition, photodiodes that have higher sensitivity (resolution) than the previous model's photocells, were used. Furthermore, to improve the S/N, the optical system was constructed so that stray light was reduced, particularly in low turbidity measurement. An aperture, a slit and a beam guide were made to prevent reflection at the light reflection section. The new turbidimeter employed the conventional measuring method that measures the ratio of scattered to transmitted light while featuring improved performance and functionality. The right angle scattered light turbidimeter has been also newly developed. It complies with specifications for NTU measurement and is used for turbidity measurement in drinking or environmental water.