This paper presents the realization of a lossy asymmetrical bandstop filter prototype on a microstrip planar structure using multiple Triplet sections. The realization of a single Triplet section on a microstrip structure is proposed and discussed. To prove the realizability, a third-order Generalized Chebyshev filtering function is used to obtain the asymmetrical response by placing zeros asymmetrically on the real frequency axis. With the multi-stage predistortion reflection mode technique, the lossy bandstop filter is synthesized as a network consisting of multiple Triplet sections of finite low Q resonators. The prototype is designed and fabricated on a microstrip, Rogers RT/Duroid 5880 substrate. There is very good agreement between simulated and measured results. © 2013 IEEE.