Backgrounds Firm tumor consistency is one of the most important factors that impede sufficient removal of pituitary macroademoas via a transsphenoidal approach. The utility of diffusion-weighted (DW) magnetic resonance imaging (MRI) in predicting the tumor consistency and successfulness of transsphenoidal resection was evaluated in this study. Methods Thirty consecutive primary cases of nonfunctional pituitary macroadenomas were prospectively enrolled. Conventional and DW MRI were done for all the patients and the apparent diffusion coefficient (ADC) values and the signal intensity of the solid tumor were determined. Intraoperative report of tumor consistency, the degree of fibrosis and percentage of collagen content were documented. The 8 weeks postoperative MRI was used for calculation of the tumor resection rate. Results The tumor consistency was soft in 10 patients (33.3 %), intermediate in 14 patients (46.7 %) and hard in 6 patients (20 %). The mean collagen content percentage was 10, 23.5 and 66 % ( p  = 0.009) and the average resection rate was 75, 43 39 % in the three groups respectively ( p  = 0.001). The mean ADC value was not significantly correlated with the tumor consistency and resection rate. Tumors with isointense to hyperintense signal on DW MRI were more commonly removable by suction and had higher resection rates than those with hypointense signals ( p  = 0.019). For ADC values within the range of 600–740 × 10 -3  mm 2 /s, a residual volume larger than 20 % of the tumor was more likely. Conclusions DW MRI was useful to predict the tumor consistency, collagen content and the chance of removal of pituitary macroadenomas through endoscopic transsphenoidal surgery, and is recommended in the preoperative patient evaluation.