Identification of a soil microorganism strain X-8, producer of ${eta}$-lactamase inhibitor, based on its morphological, physiological, biochemical and chemotaxonomical characteristics was performed. The strain X-8 was identified as Pseudomonas sp. The beta-lactamase inhibitor produced by this strain was highly achieved in fermentation medium contained glucose 0.5%, urea 0.25%, $K_2HPO_4{cdot}3H_2O;0.5%,;MgSO_4{cdot}7H_2O;0.5%,;FeSO_4{cdot}7H_2O;0.01%,;CuSO_4,;ZnSO_4,;MnSO_4;0.02%$. The beta-lactamase inhibitor was not extracted by organic solvent such as n-butanol and ethyl acetate but remained in aqueous layer. The n-butanol extract showed antimicrobial activity against M. smegmatis. The ${eta}$-lactamase inhibitor was stable at pH 7.0~8.0 and 4$^{circ}C$ for 24h. The ${eta}$-lactamase inhibitor was bound on ion exchanger Diaion WA-30 and HP-20 and eluted with 2N-$NH_4OH$ and acetone, respectively.