Computer simulations are performed to examine the effect of geometrical heterogeneity on chemical reaction occurring over a fractal surface of diffusion-limited aggregation (DLA). Eley-Rideal diffusion-limited reaction (DLA) is chosen as our model reaction system. Dynamic scaling theory, developed for surface growth model, is applied in, this work on chemical reaction model revealing two order parameters, alpha and beta, in different time domains, i.e. alpha = -0.74, beta = -0.48 for perfect sticking cases, and alpha = -0.72, beta = -0.5 for cases of lower sticking probability. Surfaces of different fractal dimensions are also considered, where the values of beta in both cases and alpha values in the perfect sticking case do not change obviously. In the cases of lower sticking probability, alpha values are decreased when fractal dimension approaches to 2. Comparisons are made to the surface roughening model where both order parameters are positive. (C) 2002 Elsevier Science B.V. All rights reserved.