Pseudomonas fluorescens is a plant growth promoting rhizobacterium that provides nutrients for growth and induces systemic resistance against plant diseases. It has been linked with a number of human diseases including nosocomial infections and bacterial cystitis. Chemotactic motility of P. fluorescens towards root exudates plays a crucial role in establishing a symbiotic relationship with host plants. The P. fluorescens chemotactic transducer of amino acids type B (CtaB) mediates chemotaxis towards amino acids. As a step towards elucidation of the structural basis of ligand recognition by CtaB, we have produced crystals of its recombinant sensory domain and performed their X-ray diffraction analysis. The periplasmic sensory domain of CtaB has been expressed, purified, and crystallized by the hanging-drop vapor diffusion method using ammonium sulfate as a precipitating agent. A complete data set was collected to 2.2 Å resolution using cryocooling conditions and synchrotron radiation. The crystals belong to space group P212121, with unit-cell parameters a = 34.5, b = 108.9, c = 134.6 Å. Calculation of the Matthews coefficient and the self-rotation function using this data set suggested that the asymmetric unit contains a protein dimer. Detailed structural analysis of CtaB would be an important step towards understanding the molecular mechanism underpinning the recognition of environmental signals and transmission of the signals to the inside of the cell.