This paper describes an experimental investigation on the effect of sample size on consolidation characteristics of fissured London Clay. Pore pressure dissipation tests on 38, 100, and 300 mm diameter samples were undertaken in the laboratory. Constant-headin situpermeability tests were conducted in four boreholes at different depths in the clay. Conventional oedometer tests on 76 mm diameter samples recovered from the same depths at whichin situpermeability tests were carried out were also undertaken. The results show that both the coefficient of compressibilitymvand the coefficient of consolidation determined in the laboratory are not significantly affected by sample size. It is concluded that estimate ofin situcoefficient of consolidation can best be made frommvdetermined in the laboratory, and fromin situpermeability measurements.Key words: consolidation, compressibility, fissured clay, permeability, size effect, testing.