Cross sections for photoabsorption of HC1 and DC1 are determined in the spectral region of 135-232 nm using radiation from a synchrotron light source. At wavelengths near the onset of absorption (λ > 200 nm), cross sections of HC1 are approximately 5-10 times larger than those of DC1. These data are used to calculate rates of photodissociation of HC1 and DC1 in the Venusian atmosphere. For the entire wavelength region measured, the rate of photodissociation of DC1 is only 16% that of HC1. The difference in rates of photodissociation contributes to the exceptionally large [D]/[H] ratio of the Venusian atmosphere. Subject headings: planets and satellites: individual (Venus) - ultraviolet: solar system.