Abstract: By comparing the MODIS LAI to field measurement and retrieved LAI from the PROSAIL physical model using TM image, accuracy of the MODIS LAI product for corn crops in Jilin Province was assessed, which could provide the basis of evaluating and using MODIS products accurately. The results show that the accuracy of the MODIS LAI product varies largely with the crop growth stages and the vegetation types. In addition, the mixed pixels were likely causing underestimation of the MODIS product for corn crops. The differences between MODIS and field measured LAI varies with different years and growth periods. After grain-filling stage, MODIS LAI values were apparently lower than estimated LAI by TM image and PROSAIL physical model. The LAI of corn crops had been underestimated by MODIS about 33%–53% and about 30%–69%, as compared with the field measurements and simulated LAI from TM, respectively. As a whole, MODIS LAI product of corn crop has much bias compared with actual LAI value, it is necessary for the validation of corn crop MODIS LAI product accuracy. This study can provide the scientific reference for the use of MODIS LAI product, and it can also be used as an approach for validating the MODIS LAI product generated by improved algorithms.