Background: Infections caused by gram negative bacilli producing β-lactamase have serious implications for both public health and infection control practices. These infections are often associated with retardation in the management with effective therapy, as β-lactam resistance often challenges empirical treatment regimens. Objectives: The study aimed to review the rates of ESBL, MBL and AmpC beta lactamases production among Gram negative bacilli and to assess the best phenotypic method that detect the resistance. Methodology: This study included 200 isolates obtained from patients admitted to different departments in Assiut university hospital. Screening and phenotypic tests which are confirmatory for resistance were done. Results: The most common type of beta lactamases in G-ve isolates by confirmatory tests was the ESBL (46%) and most common in Salmonella spp (57%) then AmpC (44%) and mostly among Serratia marcescens (83%), and lastly the metallo beta lactamase (34%) and mostly in Proteus mirabilis and Burkholderia cepacia (40%)for each of them. For detection of ESBL, Vitek2 and the ChromID™ ESBL agar were the most sensitive while CDT was more in specificity. For AmpC, disk approximation test showed more sensitivity and less specificity than Boronic acid. While for carbapenemase, the ChromID® Carba smart agar detect the highest percentage, high sensitivity is detected in the combined disk test for MBL. Conclusion: The phenotypic confirmatory tests were highly sensitive and specific and proved to be reliable methods that detect the beta lactamase resistance, genotypic tests are recommended to be a gold standard tests for increasing the specificity of the phenotypic tests.