  The first UBV(RI)_C time series photometry of the RRd star V372 Ser is
presented to determine some parameters of the star. In April, May 2007 2812 U,
B, V, R_C, I_C frames were obtained at Konkoly and Teide Observatories, 1508 V
observations were collected from the literature. Fourier fitted light curves
have been derived in all bands. The non-linearly coupled frequencies
f_0=(2.121840+/-.000001) c/day, f_1=(2.851188+/-.000001) c/d, i.e. periods
P_0=0.4712891+/-.0000002 days, P_1=0.3507310+/-.0000001 d, P_1/P_0=0.7441950,
amplitudes A_0(V)=0.15399 mag, A_1(V)=0.20591 mag, and phases have been found.
A_1/A_0=1.319+/-.008 has been found from averaging the amplitude ratio in the
different bands i.e. the first overtone is the dominant pulsation mode. From
the V observations upper limits are given for secular change of the Fourier
parameters. The period ratio and period put V372 Ser among the RRd stars of the
globular clusters M3 and IC 4499, mass, luminosity, and metallicity estimates
are given.
