Effects of pre-and postharvest treatments with potassium phosphite, potassium phosphate, and salicylic acid against the severity of gray mold disease (Botrytis cinerea) in strawberry fruits were investigated under ambient conditions. Seven B. cinerea isolates were collected from naturally infected strawberry plants and the isolate with the highest ability to cause disease was chosen for the in vitro and in vivo studies. The results showed that the treatment with potassium phosphite at concentration of 500 mg/L significantly reduced the fungal growth compared with other treatments in vitro. Also, the treatments of strawberry plants with potassium phosphite at concentrations of 250 or 500 mg/L resulted in the highest disease reduction, followed by the treatment with salicylic acid. Additionally, effects of postharvest treatments with these chemical compounds on disease reduction and biochemical attributes of strawberry fruits were evaluated during storage for 9 days at room temperature. The highest disease reduction percentage was found for strawberry fruits treated with potassium phosphite. Besides, the phenolics content and peroxidase activity of the infected and potassium phosphate treated strawberry fruits were found to be greater than those of the infected and potassium phosphite or salicylic acid treated ones at the end of storage. However, a reduction in the total soluble solids, titratable acids, and ascorbic acid contents of strawberry fruits was found for all treatment groups at the end of storage. Based on the obtained results, potassium phosphite and salicylic acid can be recommended as fungicide alternatives for extending postharvest shelf life of strawberry fruits.