This paper presents the use of polymer coated microelectrodes for the realtime conductivitymonitoring in a microchannel photoablated through the polymer without contact. Based onthis strategy, a small conductometry sensor has been developed to record in timeconductivity variation when an enzymatic reaction occurs through the channel. The rateconstant determination, k2, for the dephosphorylation of organic phosphate-alkalinephosphatase-superparamagnetic beads complex using chemically different substrates suchas adenosine monoesterphosphate, adenosine diphosphate and adenosine triphosphate wastaken as an example to demonstrate selectivity and sensivity of the detection scheme. Thek2 value measured for each adenosine phosphate decreases from 39 to 30 s-1 in proportionwith the number (3, 2 and 1) of attached phosphate moiety, thus emphasizing the sterichindrance effect on kinetics.