The non-destructive determination of plant biomass is not possible; however crop canopy sensors that determine the Normalized Difference Vegetation Index (NDVI) have the potential to estimate living biomass. Pot experiments using sand culture were conducted in 2004 and 2005 under greenhouse conditions to evaluate the effect of Nitrogen (N) deficiency on red pepper biomass and reflectance. Nitrogen stress was imposed by implementing 6 levels (20% interval) from 40% to 140% of N in Hoagland's nutrient solution in 2004 and 2005. Canopy reflectance measurements were made with hand held spectral sensors including an active red GreenSeekerTM (Ntech Industries) and passive sensors including Crop CircleTM (Holland Scientific), and Field ScoutTM Chlorophyll meter (CM1000, Spectrum Technologies, Inc.), and spectroradiometers (LI-1800, LICOR Inc.) as well as Minolta SPAD-502 chlorophyll meter for 2004 experiment. And active green GreenSeekerTM (Ntech Industries), active red and amber Crop CircleTM ACS210 (Holland Scientific), and spectroradiometers (Ocean Optics models SD2000) sensors were additionally measured in 2005 experiment. Canopy reflectance and dry weight of red pepper were measured at the different growth stages from the 30th day after planting (DAP) to 120th DAP for 2004 experiment and the 35th DAP to 123rd DAP for 2005 experiments, respectively. Dry weight of red pepper affected by nitrogen stress showed large differences between maximum and minimum values at the maturity stage, ranging from 48.2 to 196.6 g plant-1 for 2004 (120th DAP) and from 33.2 to 123.7 g plant-1 for 2005 (123rd DAP). Several reflectance indexes obtained from GreenSeeker, Crop Circle, and spectroradiometers including chlorophyll readings were compared for evaluation of red pepper biomass. The rNDVI and aNDVI, where the amber band is substituted for the red band in the rNDVI equation, by passive sensor of Crop CircleTM for 2004 experiment and by active red and amber Crop CircleTM ACS210 for 2005 experiment were the best tool for assessing differences in dry weight of red pepper at every growth stage evaluated. Especially, the rDVI and aNDVI at the critical growth stage, 78th DAP and 74th DAP for 2004 and 2005 experiment, respectively were closely correlated with dry weight, yield of green pepper, and amount of N uptake by leaves at maturity stage. This result suggested that these reflectance indexes could be used for in-season N management decisions when using real-time red pepper sensors. Ground-based remote sensing provided a non-destructive real-time assessment of plant N status and should be a useful tool for in-season red pepper N management providing both spatial and temporal information. Key words: Reflectance index, ground-based remote sensor, red pepper, dry weight.