Photoelectric UBV observations and period study of AK Herculis system

New photoelectric UBV observations of the W Ursae Majoris-type eclipsing binary AK Her are presented. The system exhibits many phenomena such as O'Connell effect, unequal depth, phase shift and different duration in secondary eclipse due to its totality, which have been studied. O'Connell effect-duration relation may be exist. The (O-C) curve has been obtained and the new light elements have been calculated. The analysis of the minima-times data of the system reveals possible sinusoidal orbital period variation (LITE). The study of the (O-C)curve, the light curves, O'Connell effect and the duration effect have led to that the system is likely a case which undergoes cyclic around the marginal contact state conservatively with mass transfers between its components, i.e.in TRO mode. This revised version was published online in July 2006 with corrections to the Cover Date.