In the present study, phytosterol profiles were used to identify adulterations of flaxseed oils from different varieties and producing areas in Qinghai Province. A combination of similarity evaluation and cluster analysis was used to distinguish pure flaxseed oil from flaxseed oil adulterated with rapeseed, peanut, sunflower, or sesame oil at concentrations between 10%-50% and discriminant analyses were used to identify the types of adulterating oils. The results showed that similarity evaluation combined with cluster analysis can distinguish pure and adulterated flaxseed oil when the concentration of the adulterant was greater than 10%. Discriminant analysis models accurately identified the types of adulterating oil in flaxseed oil when the concentration of rapeseed, peanut, or sunflower oil was greater than 20%, and that of sesame oil was greater than 30%. This study shows that the determination of the phytosterol composition and chemometrics is a valuable tool to evaluate the purity of flaxseed oil.