Public concerns of microplastic pollution have spread from aquatic environments to terrestrial ecosystems. Large amounts of microplastics have recently been detected in terrestrial environments. Until now, the effects of microplastic on the soil fauna still remain largely unexplored. Microplastics occur in various shapes, sizes and polymer types. The influence on soil organisms might depend on one of these parameters. In particular, the earthworm Eisenia fetida is likely to come into contact with microplastics while foraging. Therefore, we assessed the direct effects of three representative polymer types (PS, PA, and the biodegradable PLA) as particles and fibres (2% v/v in soil) on the life-history and oxidative stress level of the earthworm E. fetida over a period of 56 days. The ecotoxicological responses were evaluated by analysing various oxidative stress biomarkers to uncover potential direct effects on the earthworm. Also, the gut microbiome plays an important role in an organism's health. By quantifying the gut microbiome composition and activity we studied the indirect effects of microplastic exposition on the worm. As studies have shown that fibres cause severe tissue damage and increase oxidative stress, we hypothesize that worms exposed to microplastic fibres will have a reduced growth rate, reproductive fitness and health. In addition, different polymer types can cause shifts in the composition of the gut microbiome. The findings will be beneficial in estimating the effect, mechanism and hazard potential of microplastics of a specific shape and polymer on soil biota.