UBV photometry and period variations of V 839 Ophiuchi A complete period variation analysis and new light curves of V~839 Ophtogether with new ephemeris data are presented. The period variation wasfound to be dP/dt=3.1x10^{-7} d/yr. The period increment indicates thatthe conservative mass transfer rate from the less massive component tothe more massive one is 6.5x10^{-7} M_{\sun}/yr. We fitted parabolic andwe discuss the possible detection of sinusoidal curves to the (O-C)diagram and sinusoidal oscillations with period of about 20 yr andsemi-amplitude of 0.0065 day. A simultaneous solution of the B and Vlight curves was computed using the Wilson-Devinney syntheticlight-curve code. The light curve solution indicates that the A-type WUMa-type system is in contact with a filling factor of ~39%. Table 2 andTable 5 only available in electronic form: see the Editorial in A&AS1994, Vol. 103, No. 1.
