Dimeric rhodium(II) acetato (OAc), lactato, and mandelato (mand) complexes with phenanthrolines [Rh 2(OOCR) 2(NN) 2(H 2O](OOCR) 2 (R = CH 3, CH 3CHOH, C 6H 5CHOH, NN = 1,10-phenanthroline (phen) and 4,7-diphenyl-1,10-phenanthroline (dpp)) have been synthesized and characterized using electronic, IR, and NMR spectra. Cytostatic activity of these complexes against the synchronously cultivated green alga Chlorella vulgaris has been investigated. The obtained results indicate that cationic complexes [Rh 2(RCOO) 2 (NN) 2 (H 2O) 2] 2+ show higher cytostatic activity than [Rh 2(OAc) 4(H 2O) 2].