Abstract-This paper presents a dynamic mechanical analysis (DMA) of a microstructured polymer optical fiber (mPOF). The fiber material is polymethyl methacrylate (PMMA), which is widely available commercially. The DMA is made by means of sequential strain cycles produced with an oscillatory load with controlled frequency to obtain the variation of the Young's Modulus with respect to temperature, frequency and humidity for mPOFs with 2, 3 and 5-ring hexagonal microstructured cladding. Results show that the 3 different cladding structures have similar Young's modulus on the stress-strain tests performed. Furthermore, the 3-ring structure presents the lowest Young's Modulus variation with temperature among the samples tested, whereas the 5-ring structure presents a Young's Modulus variation with frequency 25% lower than the 2 and 3-rings cladding structures. Regarding the humidity sensitivity, the 2-ring structure presented a 30% lower Young's Modulus variation for a 25% humidity increase. The results obtained provide guidelines for the cladding structure choice for strain or stress sensors applications when low cross-sensitivity with temperature, humidity and frequency is desired.Index Terms-microstrutured polymer optical fiber, dynamic mechanical analysis, polymethyl methacrylate.