This work was carried out in Post-Harvest Laboratory, Horticulture Department, Faculty of Agriculture, Zagazig University, Egypt during 2015 and 2016 seasons, to determine the effect of modified atmosphere (MA) treatments on storability and quality of sweet pepper fruits during cold storage and shelf life period. Storing sweet pepper fruits in different mixtures of O₂ and CO₂ in active modified atmosphere  (AMA) containing 6% O₂+4% CO₂, 4% O₂+ 4% CO₂, 2% O₂+ 4% CO₂ and 3% O₂ +3%CO₂ as well as storing  in perforated LDPE bags at 0.50% and 0.25%  decreased fresh weight loss percentage (FWL) of fruits and maintained fruit firmness and total chlorophyll in fruit tissues  compared to passive modified atmosphere (PMA) during cold storage and shelf life periods in both  seasons. Storing sweet pepper fruits in AMA containing 4% O₂+4% CO₂ or 2% O₂+4% CO₂ decreased FWL of fruits. Moreover, storing fruits in AMA containing 2% O₂+4% CO₂ maintained fruit firmness at 28 days of cold storage and shelf life in both seasons. No decay was observed and general appearance (GA) of fruits was excellent at 28 days of cold storage in both seasons with storing in AMA, perforated low density polyethylene (LDEP) bags and PMA. Storing green pepper fruits in AMA containing 2% O₂+4% CO₂ maintained the best quality characters at 28 days at 8±1^oCand 90-95% RH. Fresh weight loss percentage and fruit decay were gradually increased with the advance of cold storage periods .On the contrary, fruit firmness, general appearance and total chlorophyll in fruit tissues were gradually decreased with the advance of cold storage periods.