Technical Abstract: The adoption of Bt corn has been largely overshadowed by concerns about their unintended effects on human health and the environment. Residues of transgenic Bt crops decomposed more slowly than their non-transgenic isolines in one laboratory study, although no mechanism to explain these observations was proposed. If Bt crop residues were to decompose more slowly in field soils, changes in carbon cycling and nutrient availability could result. We compared the in-field decomposition rates and diversity of decomposers colonizing residues of two Cry1Ab Bt corn hybrids, active against the European corn borer, with their non-transgenic isolines in litterbags placed in a Nebraska field. After five months, we found no significant differences in either the rates of residue mass loss or in the bacterial, fungal or microarthropod communities colonizing the transgenic versus the non-transgenic residues. Instead, both residue mass loss and detritivore colonizers were significantly affected by residue placement (surface versus buried) and plant part, demonstrating that environmental factors and residue quality, not the presence of the Cry1Ab protein, were the key drivers of residue decomposition and detritivore colonization in this study.