Polypropylene (PP) shows a great potential in application as recyclable cable insulation. This study investigates water absorption of isotactic polypropylene (iPP) and atactic polypropylene (aPP) as well as its effects on resistivities, and structural changes including crystal form and chemical groups for PPs before and after water absorption were also compared. Results show that with the increase of immersion time, water absorption rates of both iPP and aPP tend to increase, iPP show a higher water absorption and a maximum of 0.1% can be observed. The crystals of both iPP and aPP do not show apparent changes in the water absorption process, but the variations in chemical groups for both iPP and aPP show a similar behavior. With the increase of immersion time, the resistivities of both iPP and aPP show a decreasing tendency and a cross over takes place even though the resistivity of iPP is higher that of aPP, which maybe related to the changes in chemical groups. Moreover, Pearson correlation coefficients between water absorption rate and logarithmic value of both iPP and aPP approach –0.9, which indicates a strong relation. The findings could provide a reference for application of PP-based material in cable insulation.