The current study involves preparation number of cysteine derivatives by the reaction of cysteine with different aromatic aldehydes forming the following Schiff bases: "2-(4-bromobenzylideneamino)-3-mercaptopropanoic acid, 2- (4-hydroxybenzylideneamino)-3-mercaptopropanoic acid, 2-(4- (dimethylamino)benzylideneamino)-3-mercaptopropanoic acid and 2-(4-chlorobenzylideneamino)-3-mercaptopropanoic acid". The new prepared derivatives were identified by using spectroscopy (FTIR) and measuring their melting points. The biological activities against Proteus mirabilis were estimated using well-diffusion method around the plate then the antibacterial activities were estimated. The effects of the prepared compounds on urease activity were studied. The results showed good effect in urease inhibition. All the prepared compounds showed competitive inhibition since the value Vmax was the same and Km increased. Finaly, Vmax, Ki, Km and i % values of the enzyme was calculated using line weaver Bruk equation. It is noticed from enzymatic and biological studies that Schiff bases compounds are strong inhibitors of the urease enzyme where the(2-(4-(dimethylamino)benzylideneamino)--3mercaptopropanoic acid ) inhibition force was (Ki=0.0043 M) which is the highest inhibition force comparing with the other prepared compounds. The percentage of inhibition (%i) was equal to (96.77%).