The quality of sugar beet is affected by harmful nitrogen compounds. Although nitrogen is one of the essential elements for plants, introduction of excess nitrogen as fertilizer to the soil increases the nitrogen containing compounds in beet which deteriorates the quality of sugar production. Hence, the concentration of soluble nitrogen in beets was monitored as a routine process in the sugar industry. In this work, a low cost, but very long life time laser diode spectrometer, was developed for continuous monitoring of amino nitrogen compounds in sugar beets. A laser diode source emits monochromatic light at 635nm which is the maximum of absorption spectrum of Cu(II)-glutamine complex. A standard solution of Cu(II) ion and glutamine was prepared at pH=6.0 to calibrate the laser diode spectrometer. The formation of Cu(II)-glutamine complex was examined at pH=5.0, 6.0, and 7.0 by a continuous variations method and we found a monovalent complex, Cu(II)(glutamine) at pH=6.0, and a divalent complex, Cu(II)(glutamine)2 at pH=7.0. A continuous mixing system with a peristaltic pump and tubing was set for monitoring of harmful nitrogen in beets, besides sugar determination with a polarimeter and Na and K measurement with a flame photometer, synchronously. The calibration of the laser diode spectrometer yielded a linear correlation coefficient of R2=0.999. A negative correlation between sugar digestion and amino nitrogen content of sugar beets was found, with a correlation coefficient of R2=0.807.