The aim of this study was to evaluate the control of Alternaria rot in 'Thompson Seedless' grapes by means of modified atmosphere. Polyamide bags were compared to high density polyethylene bags, combined or not with sodium metabisulphite (SO2). Fruit from a commercial farm were selected and disinfested; then, they were injured with an entomological pin, inoculated with a suspension of Alternaria alternate at a concentration of 105 conidiam L-1 and kept in a wet chamber for 24 hours. Subsequently, grape boxes were placed inside specific bags according to the treatment and stored in a cold chamber at 2°C and 75% relative humidity during 40 days. From the 12th day of storage, the disease incidence and the following physic chemical varieties were weekly evaluated until the 40th day: weight loss, soluble solids content (SS), pH, titrable acidity (TA), SS/TA ratio, peroxidase activity, and CO2 and O2 concentrations. A completely randomized split-plot design was adopted with five replicates. Covering grape boxes with polyamide bags, even when sodium metabisulphite was not used, showed to be a feasible alternative to maintain the postharvest quality of ‘Thompson Seedless’ grapes, as well as to reduce rot caused by A. alternata.