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The objective of this study was to determine bell pepper crop-coefficient values using soil moisture sensor-based (SMS) drip-irrigation under plastic mulch in a two-year field experiment. Irrigation was applied when soil water content decreased below soil field-capacity (0.12 m3/m3 volumetric water-content). The soil water profile was monitored by a matrix (3 x 4, horizontal x vertical) of time domain reflectometry (TDR) probes. Hourly ETos was calculated using the ASCE-ET method. Transplanting occurred in early April and during the first 21 days after transplanting (DAT), irrigation was fixed at 5.5 mm/day for establishment, after which SMS-controlled irrigation started. Between day of year (DOY) 121 and 174 (final harvest) the total water application was 138 mm. No leachate was collected in the drainage lysimeters. The calculated Kc values ranged between 0.35 to 0.42 in the initial plant growth until 135 DOY. In the development stage, Kc values increased to a maximum of 0.7 and 0.87, for years 1 and 2, respectively. The crop coefficient for bell pepper did not decline during the harvest due to the fact that fruits were harvested while the plant was still green. The measured seasonal Kc values were 17% to 33%, respectively, below those reported in FAO-56, which are in accordance to the general FAO recommendations of reducing FAO tabulated Kc values by 10-30% when using plastic mulches.