The current paper presents an estimation of the undrained shear strength ($s_u$) of Busan clay through a comparison of the results of field vane and laboratory shear test results at two sites in the Nakdong River Delta. The results indicate that because of fabric effects in the clay, determining the effective overburden stress (${sigma}_{v0}{^{prime}}$) and the field vane strength ($s_{u,FV}$) based on the corrected cone resistance ($q_t$) is effective. The ratio $s_{u,FV}/{sigma}_{v0}{^{prime}}$ varied with the depositional units, independent of the plasticity index ($I_p$). In comparison to $s_{u,FV}$, combined shear strengths obtained from the consolidated-undrained compression and extension triaxial tests were slightly smaller and occasionally scattered because of the effects of sample disturbance. The laboratory shear strengths rely on the strain rate, regardless of the $I_p$. The correction factors using two different approaches were larger than those of the existing methods. For practical applications, the $q_t$-based corrected vane strengths with the correction factor (${mu}$) are thus recommended as the mobilized undrained shear strength of the clay (i.e., ${mu}s_{u,FV}/{sigma}_{v0}{^{prime}}$ of 0.23), which is similar to the corrected value of the combined shear strengths for all depths.