This paper presents calculations of the dissolution valence and the hydrogen evolution ratio during anodization of silicon as a function of the size of nanopores in porous silicon. Experimental results indicate excellent agreement with calculated relations. The data lead to the conclusions that the values of the dissolution valence and the hydrogen evolution ratio in anodization of silicon are changed from 2 to 8/3, and from 4 to 8/3, respectively, according to the size of the nanopores. We can estimate the pore sizes from these values.