Mushrooms' quality may be significantly changing depending on their type, strain, growing cycle, packing, cooling, postharvest handling (PHH), and conditions of storage. This work aimed to define the influence of the type and mushrooms' strain, the regime of the PHH by carbon dioxide on their preservation (marketability, loss of weight (LW)), changes in the chemical substances, and physiological activity (intensity respiration (IR) and heat release (HR)). Mushrooms Agaricus bisporus (AB) (strains ІБК-25 and ІБК-15) and Pleurotus ostreatus (PO) (strains НК-35 and Amycel 3000) were used for testing. Three regimes of treatment by CO2 with a concentration of 20% were applied: 2 h; 12 h and 22 h. The control was the mushrooms without treatment by CO2. Changes in the chemical substances such as dry matters (DM), protein nitrogen (PN), and ascorbic acid (AA) in the researched mushrooms were observed. The best result of mushroom preservation was provided by the regime of CO2 treatment during 12 h. The yield of marketable AB was 94.9% (IBK-25) and 94.2% (IBK-15) comparison to control 93.5%, and 92.5%, respectively. The regime of PHH 2 h almost has no influence but 22 h harmed this indicator. PHH of mushrooms by carbon dioxide was promoted to preserve the DM and increasing concentration of CO2 was supplied better results. Thus, DM at the end of storage in the AB of strain IBK-25 depend on the regime were 8.5, 8.6, and 8.4%, against – 8.3% in the control variant. Significant quantitative changes in the PN and AA as a result of treatment by CO2 were not established. PHH also affected the IR and HR. The increased duration of treatment by CO2 inhibited the intensity of physiological processes in the mushrooms. But, as in previous cases, the best result was provided PHH by 20% CO2 during 12 h. Similar trends of treatments effect by carbon dioxide were observed in the mushrooms of PO.