Many biomedical applications require high sensitivity for measuring strain induced in biomechanical structures. Although current metallic foil strain gauges are capable of measuring strain deformations, their low sensitivity and relatively large size render them unsuitable for implantable and wearable application. In this paper, we present a novel nanocomposites strain sensor using Poly(L-lactide) (PLLA) as a host polymer matrix and multi-walled carbon nanotubes (MWNTs) as filler. The PLLA matrix improves load transfer across the nanotubes by means of better interfacial bonding between polymer and carbon nanotubes filler, thus endowing the nanocomposites material with excellent piezoresistive property. Experimental results using a fabricated nanocomposites strain sensor is presented demonstrating its linear response and high gauge factor. Due to biocompatibility and biodegradability of PLLA, the proposed sensor is attractive for many biomedical and wearable applications.