The photodecay rate k of methylene blue catalyzed by well-aligned TiO2 nanorod arrays is found to follow a quasi-scaling relationship with the nanorod length h, k proportional to Mh(xi) + N, where M and N are constants, and xi = 1.0 +/- 0.5. A theoretical model based on first-order surface photoreaction predicts that this scaling behavior is directly related to the morphological scaling, xi = 1 + p + gamma, where p = 0.6 +/- 0.3 and gamma = -0.3 +/- 0.3 are the scaling exponents for the nanorod circumference and density versus length. This prediction is consistent with the experimental results. (c) 2009 Elsevier B.V. All rights reserved.