The soil behavior is rate-dependent as observed in the laboratory and field tests, and the undrained shear strength of clay is shown to increase with the strain rate in different shear modes. In practical situations, the foundations can be loaded at various time and rate scales, which will result in a wide range of magnitudes and inhomogeneous distribution of strain rates in the surrounding soil. This may cause difficulties in calculating the undrained bearing capacity of clay using the undrained shear strength from standard laboratory and field tests at a reference strain rate. In addition, the rate-dependent soil behavior will also affect the interpretation of in situ tests conducted at different loading rates (e.g., CPT, T-Bar, and pressuremeter tests) using procedures based on rate-independent soil models. This paper investigates the effect of loading rate on the undrained bearing capacity of clay using finite element analyses and a rate-dependent constitutive model, the MIT-SR, based on two classical problems in soil mechanics (i.e., the deeply-embedded rigid pile/pipe section, and the rigid strip footing). Computed results suggest that the undrained bearing capacity of clay is strongly affected by the loading rate of foundations, which is consistent with the model and field tests. It also highlights the difficulty to select appropriate undrained shear strength used for practical design, and the uncertainty to interpret field tests using bearing capacity factors derived from analytical solutions.