Enzyme sensors using L-amino-acid oxidase (EC 1.4.3.2), D-amino-acid oxidase (EC 1.4.3.3) L-lactate dehydrogenase (EC 1.1.1.27) and D-lactate dehydrogenase (EC 1.1.1.28) with osmium complex were developed for measuring L-phenylalanine, D- phenylalanine, L-lactic acid and D-lactic acid in optical isomers, respectively. The platinum micro-sensors (platinum diameter, 30 μm) for amino acids were etched in hot aqua regia to create a cavity at their tip. A porous composite material prepared from acetylene black and Teflon emulsion was packed into the tip of the platinum sensors and the redox mediator [O_s(bpy)₃](PF₆)₂ was monitored by cyclic voltammetry in the potential range 200 - 900 mV. The micro-sensors were dipped overnight in buffer solution containing the desired enzyme to immobilize it on the tip by adsorption method. On the other hand, the tips of platinum sensors (platinum diameter; 0.5 mm) for lactic acids were packed with the porous composite material above-mentioned. Electrostatic coupling of the redox mediator, into the Nafion layer was achieved by dipping it into osmium complex solution.  These were dipped into a buffer of containing enzymes, and then into albumin solution and glutaraldehyde solution to immobilize the enzyme by cross-linking. Calibration curves for measurements, the effects of pH, temperature, and concomitant compounds, the effects of the other optical isomer on measurements, the life-time of the sensors, and their availability for measuring L-amino acids in urine were examined. Under optimal conditions, the response of sensors was linear in the concentration ranges of 3.3 - 240 μg/ml L-phenylalanine, 0.83 - 17 μg/ml D-phenylalanine, 0.9 μg/ml - 1.26 mg/ml L-lactic acid and 9 ng/ml - 2.25 mg/ml D-lactic acid. The sensitivities of the sensors were constant for more than one month.