The quantification of crystallinity is necessary in order to be able to control the milling process. In this study, the changes in the amount of residual crystallinity of ball-milled anhydrous β-lactose (β-LA), for periods up to 60 min, were evaluated by differential scanning calorimetry (DSC) and by terahertz pulsed spectroscopy. The percentage of residual crystallinity using DSC was estimated by two methods: The first method was based on the measurement of the melting of the crystalline part, while the second was based on the measurement of the devitrification of the amorphous part. Peaks in THz spectra, related to the residual crystalline material were analyzed by two methods: (1) area under peak and (2) partial least square. The milled samples of β-LA show a monotonic decrease in crystallinity with milling time, although the quantitative analysis performed by different techniques reveals very different results. THz technique gives significantly lower estimates for % crystallinity (in the early time period) than that calculated from the DSC data, possibly because of the recrystallization of amorphous form during sample preparation. The comparison of residual crystallinity of β-LA with its hydrated counterpart [i.e., α-lactose monohydrate (α-LMH)] has shown that the amount of amorphous material produced from the α-LMH is 20–30 % greater than from β-LA at extended milling times (i.e. 60 min).