Polycrystalline SrRu(1-x)Mn(x)O(3) (0≤x≤1) perovskite oxides have been prepared by a conventional solid-state reaction technique. Magnetic and magnetotransport properties are measured using a superconducting quantum interference device (SQUID, Quantum Design MPMS) over a temperature range of 4-300 K. The substitution of Mn ions for Ru drives the system from a ferromagnetic state, SrRuO(3), to an antiferromagnetic state, SrMnO(3), which is basically similar to observations in single-crystal SrRu(1-x)Mn(x)O(3) (Cao et al 2005 Phys. Rev. B 71 035104). However, the measurement of dc magnetization and ac susceptibility indicates that magnetic phase transition with x is more complicated and pronounced than those in single crystals. The phase transition process as temperature is reduced covers paramagnetism-antiferromagnetism (PM-AFM), paramagnetism-ferromagnetism (PM-FM) and ferromagnetism-cluster glass-spin glass (FM/CG/SG) etc. In particular, we observe a large low-temperature magnetoresistance (MR) of -41% for the sample x = 0.55, which is the largest MR measured in Mn-doped SrRuO(3). The experiment has verified that the large MR stems predominantly from a unique spin glass state in the polycrystalline alloy. These results substantiate that Ru-based oxides doped with 3d/4d transition metals have the potential for use in spintronics devices due to their adjustable phase transition, depending upon the level and nature of 3d/4d ion doping.