In oral tongue cancer, tumor depth is crucial for cervical lymph node metastasis. There is no standardized method to predict tumor invasion or deciding who should undergo selective neck dissection. In this study, calculated MRI invasion depth was compared with histopathologic (HP) invasion depth to find a correlation, and determine a cutoff value of invasion depth that predicts occult neck node metastasis. 50 patients, diagnosed with T1 or T2 oral tongue cancer originating from the lateral border of the tongue, underwent MRI screening and received surgical excision as primary treatment. MRI and HP invasion depths were compared and the cutoff value determined. The invasion depth to determine the presence of nodal metastasis where summation of specificity and sensitivity was greatest was 8.5mm HP, 10.5mm in T1 weighted enhanced axial image, and 11.5mm in T2 weighted MRI axial image. The relation coefficient of T2 weighted MRI invasion depth and HP depth was 0.851, and accuracy 84%, all of which showed higher correlation compared with T1 weighted enhanced axial image. HP depth was significantly correlated with survival rate. The measurement of invasion depth using MRI is a prerequisite for determining a surgical plan in early oral tongue cancer.