This paper investigates the results obtained from a series of K-consolidated undrained triaxial tests, which were carried out on marine clay specimens under different stress histories and strain rates. All marine clay specimens were prepared from a slurry state and pre-consolidated in a consolidometer under a vertical pressure of 100 kPa. The specimens were then compressed to the same initial effective pressure of 400 kPa. Different over-consolidation ratios (= 1, 2 and 4) were achieved by unloading to 400, 200 and 100 kPa, respectively. After completing the K-consolidation, specimens were sheared at three rates (= 0.1%/h, 1%/h and 10%/h). The responses of the marine clay under different strain rates and the influence of stress histories under K conditions are discussed. The results show that higher strain rates tend to result in higher undrained shear strengths and lower pore pressure for different over-consolidation ratios under K conditions. Conversely, higher over-consolidation ratios tend to result in lower shear strengths for all the strain rates. Further, two rate parameters used to study the strain rate effects are also discussed and interpreted, and the suitable rate parameters of the reconstituted clay are recommended in designs for the marine clay.