Power consumption for a paddle impeller with two large blades was measured in shear-thinning fluid. The test fluid was carboxymethyl cellulose (CMC) solution. The Metzner-Otto constant k(s) was estimated by using the Metzner-Otto method (1957). The constant k(s) increased with increasing impeller diameter. The estimated (k)s showed a good agreement with the values correlated by the equation of Kamei et al. (1994).