This study was conducted in 2015 and 2016 to investigate potential use of crop water stress index (CWSI) in irrigation scheduling for drip-irrigated pumpkin seed plants. Six different irrigation levels (I-0, I-20, I-40, I-60, I-80 and I-100) were used. Amount of irrigation water applied to plants varied between 24.0-258.4 mm in 2015 and between 13.0-470,2 mm in 2016. Plant water consumptions (ET) varied between 256-479 mm in 2015 and between 227-628 mm in 2016. The greatest seed yields (1417 kg/ha in 2015 and 1306 kg/ha in 2016) were obtained from Iloo treatments and the lowest seed yields (470 kg/ha in 2015 and 427 kg/ha in 2016) were obtained from Io treatments. In 2015, water use efficiency (WUE) values varied between 0.18-0.30 kg/m(3) and irrigation water use efficiency (IWUE) values varied between 0.55-0.89 kg/m(3). In 2016, WUE values varied between 0.19 -0.24 kg/m(3) and IWUE values varied between 0.28-0.71 kg/m(3). The average lower limit baseline equation for CWSI calculations was identified as T-c-T-a = -2.3728 x VPD + 4.4254. CWSI values varied between 0.24-1.0 in 2015 and between 0.08-0.93 in 2016. CWSI significantly correlated with seed yield, leaf area index (LAI), leaf water potential (LWP), oil and protein content. It was concluded based on present findings that CWSI could reliably be used in irrigation scheduling and yield estimation of pumpkin seed plants.