In order to establish a particle number concentration standard and the related calibration technology in liquids, a new particle counter based on the simultaneous detection of scattered light and fluorescence was examined. Sample particles from 2 to 10 micrometers in diameter were dyed. By making use of the fact that bubbles make no coincidence signals between scattered light and fluorescence on the other hand particles make coincidence signals, we could distinguish particles from bubbles. And we can establish the particle number concentration and the calibration technology in liquid. Using this system, fluorescence could be measured at 525 nm, 625 nm, or 675 nm as well as at 575 nm. To examine the electric counting error and error due to stray light counting, the four channels were compared. The difference in counting between each of the channels was less than 0.1% in relative standard deviation. To evaluate the reliability of the particle counts obtained with this system, the obtained values were compared with counts obtained using a microscope. With a microscope, the total area was manually scanned for the total counting to reduce the statistical uncertainty. The results of both methods were in good agreement, with a counting efficiency of 100% plus or minus 10% for 2 micrometer particles, and of 100% plus or minus 5% for 10 micrometer particles. The difference in the repetition of the new counter was less than 1%.