  Results from optical CCD photometric observations of 13 pre-main-sequence
stars collected during the period from February 2007 to November 2020 are
presented. These stars are located in the association Cepheus OB3, in the field
of the young star V733 Cephei. Photometric observations, especially concerning
the long-term variability of the stars, are missing in the literature. We
present the first long-term $V(RI)_{c}$ monitoring for them, that cover 13
years. Results from our study indicate that all of the investigated stars
manifest strong photometric variability. The presented paper is a part of our
program for the photometric study of PMS stars located in active star-forming
regions.
