The preparation of two electrochemical (potentiometric and amperometric) phosphate biosensors is described and compared. Purine Nucleoside Phosphorylase (PNP) and xanthine oxidase (XOD) were co-immobilised via entrapment into polypyrrole (PPy) films by galvanostatic polymerization. Polypyrrole entrapment was achieved with 0.5 M pyrrole by using a polymerisation time of 200 sec and a mole ratio of 1:8 (6.2 U mL-1 XOD: 49.6 U mL-1 PNP) inboth biosensors. Sensitive amperometric measurements were compared with those of potentiometric measurements obtained for PPy-PNP-XOD-Fe(CN)6 4- biosensors. A minimum detectable concentration of 1.0 μM phosphate and a linear concentration range of 5-20 μM were achieved with potentiometric PPy-PNP-XOD-Fe(CN)6 4- biosensor. In comparison, a minimum detectable concentration of 10 μM and a linear concentration range of 0.1-1 mM were achieved with amperometric biosensor. The presence of uric and ascorbic acids had the least effect on the performance of the amperometric and potentiometric PPy-PNP-XOD-Fe (CN) 6 4 biosensors, therefore will not have any effect on phosphate measurement in both biosensors at levels normally present in water.