The present study aims to predict the oil quantity in % using Near‐infrared spectroscopy (NIRS) directly from spectral data acquired on rapeseeds (Brassica napus). In total 637 samples were used to construct and test the mathematic model. The correlation coefficient (R2) between the NIRS predicated results and the chemical extraction method was .98, .97, and .96 for the calibration, cross validation, and external validation, respectively. For external validation, the average relative error and the mean absolute error was 0.78 and 2.02%, respectively, compatible with those of chemical extraction method. Further determination suggested that 1.5 g was the minimal quantity of sample loading to obtain stable results and the NIRS method showed a similar repeatability to the chemical extraction method. Taken together, NIRS method enables the rapid detection of oil quantity of intact B. napus seeds. Practical applications The present study constructed a mathematic model for the measurement of oil content of rapeseed using the NIRS technology. Compared with the traditional method for oil content determination using the chemical extraction, the NIRS method is cheaper, safer, more rapid, and convenient. It shows similar repeatability to the chemical extraction method and needs not to destroy the samples. Thus, the method raised in the present study could be used to detect the oil content of intact rapeseeds in food and breeding industries.

Content of oleic acid varied greatly in rapeseed. When rapeseeds with broad range of oleic acid content were used for calibration, models of near‐infrared reflectance spectroscopy (NIRS) showed qualified accuracy. To further increase the accuracy of models, the present study narrowed the range of oleic content in calibration samples and only focused rapeseeds with oleic acid content ranging from 55 to 81%. Finally, external validation showed higher accuracy of the model for oleic acid than previous models, with the RSQ of 0.995. Meanwhile, models for linoleic and linolenic acids were also constructed, both showing high RSQ (0.929 and 0.907). These NIRS models could be used for fast determination of fatty acid contents in rapeseeds during agricultural and breeding practices. Practical applications The NIRS method has advantages of rapidity, high efficiency, reliable results, no drug contamination, and no damage to materials. The models constructed in the present study could be used to determine contents of oleic, linoleic, and linolenic acids in rapeseeds. This method can determine several quality parameters with only a small amount of sample at the same time. It is of great significance to save manpower, materials and improve the analysis efficiency in plant breeding applications and rapeseed quality analysis. It is an effective detection method for screening rapeseed breeding materials, analyzing fatty acid components, and quality of rapeseeds.