Condensation of rhodanine ( 1 ) with pyrazol-3(2 H )-one derivatives ( 2a – f ) gave 5-substituted-2-thioxo-1,3-thiazolidin-4-one derivatives ( 3a – f ). Reaction of compound ( 1 ) with 2-arylmethylidene-malononitrile ( 4a – d ) yielded the unexpected derivatives ( 5a – d ). The latter compounds were subjected to cyclization reactions with malononitrile under different basic conditions, hydroxylamine hydrochloride and/or thiourea to furnish the fused thiazole derivatives ( 6a – d ) and ( 8 – 10a – d ). Coupling of ( 1 ) with diazotized aromatic amines ( 11a – c ) in pyridine afforded the arylhydrazones ( 12a – c ). Fusion of latter compounds with malononitrile afforded the thiazolopyridazine derivatives ( 13a – c ). The structures of the newly synthesized compounds were elucidated via spectral data and elemental analyses. The in-vitro cytotoxic activity of compounds ( 3a – f ) against the cell line MCF-7 was evaluated. Also, the synthesized products were investigated for their antibacterial and antifungal activities against six standard organisms including the G⁺ bacteria, Staphylococcus aureus and Bacillus subtilis , G⁻ bacteria, Escherichia coli and Proteus vulgaris in addition to fungi, Candida albicans and Aspergillus flavus .