The disposal of effluent sludge is a difficult problem throughout the world. Agricultural utilization of sludge as resources is one option. However, high levels of heavy metals pose difficulties in the safe use of sludge. To reduce the heavy metal content of sludge, a technique combining remediation with earthworms and hyperaccumulators has been suggested to be effective and is drawing the attention of scientists in the field. Therefore, an experiment was conducted to evaluate effect of earthworms on heavy metals in sludge. In the experiment, sludge was collected from a wastewater treatment plant in Dongguan, and 400g (dry weight) fresh sludge was put in a plastic pot. The earthworm Eisenia fetida was used. Twenty healthy earthworms were added to each replicate pot. Each earthworm weighed about (0.35±0.03)g, with total earthworm weight about 7g per pot. Control pots with no earthworms were set up too. Sludge measurements were made, including heavy metal speciation, redox conditions, chemical properties, enzymatic and microbial properties. The results showed that the earthworm Eisenia fetida could survive well and grow in the sludge. By the 20^th day, the earthworm weights were approximately 0.55g each (10.66g per pot). In the treatments with earthworms, the amount of Cu, Zn, Cd, and Ni in the form of residue, organic, and Fe-Mn bound metals significantly decreased, and those in the forms of exchangeable and water soluble metals significantly increased. However, earthworms had no significant effect on the speciation of Pb and Cr. The earthworms also significantly reduced the amount of total reductive substance, active reductive substance and active organic reductive substance, but had no significant effect on the ferrous iron (Fe²⁺), free iron oxide (Fe₂O₃), amorphous iron (Fe₂O₃) and complex iron (Fe) content. The pH of sludge with earthworms (pH = 5.62) was significantly higher than that of the control group (pH = 5.20) by the 80^th day, but both groups had significantly lower pH than the original sludge (pH = 6.49). The total organic carbon and fulvic acid content were reduced by earthworms, and earthworms promoted the conversion of ammonium nitrogen to nitrate nitrogen. Metabolic quotient and catalase were significantly increased, while microbial biomass carbon, invertase, and fluorescein diacetate enzymes were significantly reduced in the earthworm treated sludge. These findings suggest that earthworms reduced the number of microorganisms in the sludge, while increasing microbial activity. With the addition of earthworms, the activation of heavy metals in sludge had a significant negative correlation with reductive substance content, but had a significant positive correlation with microbial activity. In summary, earthworms could facilitate the activation of heavy metals in sludge, and improve its fertility. Thus, addition of earthworms to sludge could provide favorable conditions for the growth of hyperaccumulators, other plants, and the uptake of heavy metals from sludge.