A monolithic polydimethylsiloxane (PDMS) spectroscopic analyzer was fabricated using a mold, which was fabricated by 3D printer. It detected the fluorescence signal from a sample sealed in a PCR tube. However, in order to perform high sensitivity measurement for detecting a small amount of samples, the scattering light and the stray light must be intercepted with high extinction ratio. It is achieved by designing and fabricating an optical system of a complex folding for extracting only the signal light. In this study, we report about design and fabrication of a folding monolithic PDMS spectroscopic analyzer using 3D printer.