Estimation of the structural weight of an Unmanned Combat Aerial Vehicle (UCAV) during conceptual design has proven to be a significant challenge mainly due to its unconventional configuration. We investigate development of a customised approach for structural weight estimation of UCAV based on statistical weight of the manned fighter’s components by applying minor modifications on weight formulations of fuselage, wing, empennage, power plant and landing gear. The modifications are applied by considering the corresponding differences between manned fighters and UCAVs such as manned requirements and mission variances. Some new empirical formulas for estimating the weight of UCAV’s components are proposed. Results for the empty weight estimation are validated against actual values of some well-known UCAVs. Moreover, the structural weight is validated against the benchmark UCAV case studies. The results show that the ratio of structural to takeoff weight for UCAVs is approximately between 20% to 10%. Finally, a generalised equation is developed for estimating the structural weight of UCAVs in conceptual design phase.