This work investigates the moisture diffusion behavior of bio-based balsa wood and balsa core sandwich structures. All the special dog-bone balsa wood and sandwich specimens were immersed in water at room temperature to saturation, and the moisture absorption kinetics were identified analytically and numerically. It was found that the final saturated MC in the GFRP-balsa sandwich was only 18 % of that in the pure balsa wood. This suggests that the assembly of environmentally friendly balsa wood and conventional Glass-Fiber-Reinforced-Polymer (GFRP) skins may be a good alternative to the pure hydrophilic wood materials or high-carbon-footprint laminates. Interestingly, Fickian behavior was observed in the moisture diffusion process of pure balsa wood, while Non-Fickian behavior was discovered in the more complex sandwich. Accordingly, two different moisture diffusion models, the Fickian model and the Dual Fickian model, were considered to calculate the moisture diffusion coefficients and saturated moisture absorption capacity of the balsa wood and the sandwich, respectively. Moreover, the numerical model has demonstrated that the mesh size of the balsa wood core significantly impacts the accuracy of the prediction.