Embryonic development involves the interplay of driving forces that shape the tissue and the mechanical resistance that the tissue offers in response. While increasing evidence has suggested the crucial role of physical mechanisms underlying embryo development, tissue biomechanics is not well understood due to the lack of techniques that can quantify the stiffness of tissue in-situ with 3D high-resolution and in a non-contact manner. In this work, we used two all-optical technique, optical coherence tomography (OCT) and Brillouin microscopy, to map the longitudinal modulus of the neural tube tissue of mouse embryo in-situ. We found the tissue stiffens significantly after the closure of the neural tube at cranial regions by comparing embryos at E 8.5 and E 9.5. In addition, we observed that the region of fusion following neural tube closure is softer than the adjacent neural folds, and the neural folds show a modulus gradient along dorsal-ventral direction. Furthermore, we found the overlaying ectoderm is much softer and more pliable than the closed neural tube, and thus can be distinguished based on its mechanical properties. In conclusion, we demonstrated the capability of OCT and Brillouin microscopy to quantify tissue modulus of mouse embryos in-situ, and observed a distinct change of tissue modulus during the closure of cranial neural tube, suggesting this method could be helpful in investigating the role of tissue biomechanics in the regulation of embryo development.