The B3LYP functional and CASPT2 method have been applied to investigate the geometrical and electronic structures of eta(2)(S-2)MnS-/0, eta(2)-(S-3)Mn-/0, and MnS3-/0 isomers of MnS3-/0 clusters. The ground state of the anionic cluster is computed to be the B-5(2) of eta(2)-(S-2)MnS- isomer, whereas that of the anionic cluster is calculated to be the B-4(1) of the same isomer. The photoelectron spectrum of MnS3- cluster is interpreted by electron detachment processes from the most stable eta(2)-(S-2)MnS- and from the metastable eta(2)-(S-3)Mn- and MnS3- isomers. The first and second bands with low intensities are, respectively, attributed to the (7)A' -> (6)A' and (7)A' -> (8)A' transitions within the eta(2)-(S-3)Mn-/0 isomers. The third band with the highest intensity in the spectrum can be assigned to the B-5(2) -> B-4(1), B-5(2) -> B-6(1), and B-5(2) -> (4)A(2) transitions within the most stable eta(2)-(S-2)MnS-/0 isomers, the B-3(1) -> (2)A(1) transition within the metastable MnS3-/0 isomers, and the (7)A' -> 3(6)A' transition within the metastable eta(2)-(S-3)Mn-/0 isomers. Because the eta(2)-(S-2)MnS- is computed to be the most stable isomer of the MnS3- cluster, we believe that the highest intensity third band in the spectrum is mainly the result of electron detachments from this isomer.