In this study, the effects of different treatments of the oat slurry on the nutritional, functional, and sensorial properties of oat milk were evaluated. The sprouting and sprouting–acidic treatments have the highest oat milk yield (91.70%) and protein extraction yield (82.74%), respectively. The protein concentrations of alkali, sprouting–acidic, and α-amylase–alkali treatments were significantly (p < .05) higher than other treatments. The alkali treatments showed higher fat content (0.66%). In addition, acidic and alkali treatments in single or combined with other treatments showed the highest dry matter and energy value. The carbohydrate content of α-amylase–alkali treatment (4.35%) was higher than other treatments and also, all acidic treatments showed higher ash content (>1) compared to the other treatments. Furthermore, the sprouting–α-amylase and acidic–α-amylase showed the lowest starch (0.28%) and the highest reducing sugar content (3.15%) compared to the other treatments, respectively. Moreover, the α-amylase–alkali treatment showed the highest total phenolic content and antioxidant activity (342.67 mg GAE/L and 183.08 mg BHT eq/L, respectively). Furthermore, sensory evaluation of most treatments showed acceptable scores (≥7) for consumers, especially in the case of α-amylase, sprouting, and α-amylase–sprouting treatments. Results show that the different treatments had different effects on the nutritional, functional, and sensorial properties of oat milk. In conclusion, from the nutritional and functional point of view, the two-stage treatments were more effective than singular treatments on investigated factors proposing their application in functional plant milk preparation.