This study presents a novel in-situ Young’s modulus measurement technique of polydimethylsiloxane (PDMS) microfluidic chips that are designed to measure fluid viscosities. In such chips, viscosity can be accurately determined once the Young’s modulus of PDMS is also known. Yet, the Young’s modulus values of elastomers are highly dependent on their chemical composition and curing temperature. The presented approach involves integrating a piezoelectric sheet underneath the chip, oscillating the chip through sweeping the drive frequency, and monitoring the blur and speckle contrast of the pillar via an external camera. A local maximum in the blur and speckle contrast is achieved at the fundamental resonance of the pillars, from which its Young’s modulus is predicted. The experimental results validate the relationship between the Young’s modulus of PDMS and base polymer:curing agent ratio, curing time, and temperature, demonstrating that it could be measured optically. Six different PDMS microfluidic chips prepared by curing elastomer at different temperatures and using different base polymer to curing agent ratios, 5:1, 10:1, and 20:1, were utilized. The Young’s modulus of the prepared sample microfluidic chips varied within the range of 0.72 to 3.64 MPa. The successful measurement of the Young’s modulus of PDMS using the proposed techniques demonstrates its potential in determining the mechanical properties of fluidic chips in-situ, with a low-cost and simple setup.