Near infrared spectroscopy (NIRS) is a non-destructive technique for fruit quality assessment. This study applied NIRS to assess internal quality of Japanese pumpkin fruit during maturation. Japanese pumpkin fruit (Cucurbita maxima) were harvested at three stages of fruit maturation, namely, immature, mature and overmature, i.e., 40, 50 and 60 days after fruit set (DAFS). It was found that there was a possibility to use short wavelength region of near infrared radiation (700-1100 nm) to determine quality of Japanese pumpkin in terms of total soluble solids (TSS). The spectra were measured by NIRSystem 6500. Partial least squares regression (PLSR) was introduced to develop prediction models for the aforementioned parameters. The best PLS model for quality assessment of Japanese pumpkin fruit was found in TSS, resulting the coefficient of determination (R2) of 0.77. The prediction model also provided low values of SEC, SEP and bias which were 0.62%, 0.96% and 0.13%, respectively.