Cells of Pseudomonas bacteria having a high nitrile hydratase activity can be obtained in a high yield by adding to a culture medium at least one .alpha.-amino acid, except for cysteine or cystine alone and a combination of these .alpha.-amino acids alone, in the preparation of cells of bacteria having nitrile hydratase activity by cultivating under nitrile hydratase-inducing conditions Pseudomonas bacteria capable of producing nitrile hydratase.