The paper summarizes the results from undrained triaxial compression tests on Merville clay, a highly over-consolidated clay at Merville in the north of France. The specimens were prepared in four different over-consolidation ratios (OCR=7, 14, 28, 56) and, for each OCR, undrained shear tests were performed using three or four axial strain rates varying from 0.26 %/h to 25.89 %/h. The strain-rate dependency of the undrained stress level q/qf, the pore pressure, the effective stress path and the stress ratio q/p' were investigated. The undrained shear strength was found to increase with the strain rate. The shear band formation during loading was observed for all strain rates. For each OCR test series, a linear relationship between the normalized peak deviatoric stress and the strain rate was obtained in the semi-logarithm plane. As OCR increases, the slope of best-fitting line for the linear relationship increases. Therefore, the strain rate influence on the normalized undrained shear strength is greater for higher OCRs.