Selected area electron diffraction patterns of an Al-20%Ag alloy including γ' or γ precipitates have been examined at several angles of incidence and it has been concluded that the appearance of {00.1} spots from the precipitates results from dynamical multiple reflection. The result for the γ' precipitates is in contrast with previous reports in which these spots were considered to be superlattice spots ( e. g. , Nicholson and Nutting, 1961). In this brief report, it is emphasized that the attentions should be paid for dynamical interaction in interpreting electron diffraction patterns.