The results of UBV photoelectric observations of 12 symbiotic stars have been considered. It must be noted that their light-curves are very different (irregular, regular, of Mira Ceti type) and, in the two-colour diagram (B – V)–(U – B), all these stars are located rather far to the right from the main sequence. The photometric peculiarities of symbiotic stars just mentioned can be explained by assuming that they are binary systems.