PURPOSE: To easily manufacture a flexible print circuit sensor assembly and improve the cost-performance of the assembly by fixing photodetectors and light emitting diodes to conductor circuits formed on a flexible sheet of polyester, etc., and folding the circuits.

CONSTITUTION: A plurality of circuits 2 are formed on a flexible sheet 4 of polyester or polyamide by using the print board technique. Each circuit 2 is composed of a pair of copper strips 6 and 7 separated from each other at a fixed interval and the terminals 8 and 9 and 14 and 15 of the strips 6 and 7 respectively house photoelectric detectors 18 and light emitting diodes 24 and 25. After a nonconductive tape is fixed on the sheet 4, individual circuits 2 are punched or cut. Then each cut circuit 2 is folded so that the photodetectors 18 can be faced to the diodes 24 and 25 at a fixed interval. Each circuit sensor 2 is connected to an oxygen meter through terminals 10-11 and 16-17 and attached to the tissue of a patient, such as that of the finger or ear so as to measure the blood characteristic of the tissue.