Egypt is considered one of the main strawberry producer's countries. Grey mould, caused by Botrytis cinerea, is a destructive disease resulting in significant losses in strawberry production worldwide. Fruits might be infected in the field, storage and transport. Management Approaches for the pathogen in strawberry depends mainly on using protective fungicides. Boscalid is a new broad-spectrum fungicide used to control B. cinerea in strawberry. Recently, lack of efficiency of the fungicide reported in many countries. The current study aims to detect Botrytis cinerea resistant isolates to boscalidin the main strawberry production governorates in Egypt (Beheira, Ismailia and Qalyubie) between 2019 and 2021. 269 isolates were collected and tested to distinguish resistant isolates. Sensitivity of a set of resistant and sensitive isolates was measured by determining the effective concentration that inhibits 50 % of mycelial growth. The results showed that, 225 (83.6%) isolates were resistant to boscalid while, only 47 (16.4%) isolates were sensitive. Monitoring of resistance frequency revealed that there were remarkably increasing in resistance frequencies to boscalid in B. cinerea isolates during 2019 and 2021 seasons as it was 84.03% in 2019 while it reached to 98.87% in 2021. 17 Bos^S sensitive isolates randomly selected were used to determine the EC₅₀ for boscalid using mycelial growth inhibition assay and the EC₅₀ values ranged from 0.0067 to 1.14 µg/ml with a mean of 0.29 µg/ml. While, the EC₅₀ values for17 Bos^R resistant isolates randomly selected ranged from 2.1 to 16.2 µg/ml with a mean of 7.3 µg/ml.