This study is about multi wall carbon nanotube (MWCNT) aspect ratio (η) impact on polyisoprene-MWCNT composite electrical resistance and chemoresistivity. The composite has been produced utilizing MWCNT with η = 12500 and η = 40. Besides MWCNT powder electrical resistance dependence of temperature has been measured and characteristic MWCNT type determined. We found that long MWCNT (η = 12500) are semiconducting, but short MWCNT (η = 40) metallic. The composite was produced gradually increasing MWCNT concentration. Afterwards electrical conductivity of the composite was measured and electrical percolation curves obtained. Applying statistical percolation scaling law to experimental data, percolation threshold (fc) and critical index (t) was determined. Despite the fact that long MWCNT are semiconducting and greatly entangled as shown by scanning electron microscopy images, electrical conductivity emerges in the composite at lower MWCNT concentration (fc = 3.15 wt%). But if short MWCNT (metallic with needle like structure) are utilized us filler, the composite electrical conductivity is lower and percolation threshold is obtained at filler concentration 5.8 wt%. Polyisoprene-MWCNT composites were exposed to volatile organic compounds (VOC) and electrical resistance change in time observed. Both produced composites have VOC sensor effect, that is, the composite electrical resistance increases in the presence of VOC due to tunnelling current decrease between adjacent MWCNT. VOC induced polyisoprene swelling and local inter distance increase between MWCNT is the reason for tunnelling current intensity reduction.