Picosecond pulse radiolysis measurements using a pulse-probe method are performed to measure directly the time-dependent radiolytic yield of the OH center dot radical in pure water. The time-dependent absorbance of OH center dot radical at 263 nm is deduced from the observed signal by subtracting the contribution of the hydrated electron and that of the irradiated empty fused silica cell which presents also a transient absoption. The time-dependent radiolytic yield of OH center dot is obtained by assuming the yield of the hydrated electron at 20 ps equal to 4.2 x 10(-7) mol J(-1) and by assuming the values of the extinction coefficients of e(aq)(-) and OH center dot at 782 nm (epsilon(lambda=782 nm) = 17025 M-1 cm(-1)) and at 263 nm (epsilon(lambda=263 nm) = 460 M-1 cm(-1)), respectively. The value of the yield of OH center dot radical at 10 ps is found to be (4.80 +/- 0.12) x 10(-7) mol J(-1).