The present invention relates to an antibody-fluorescent dye conjugate capable of cancer cell-specific fluorescence imaging diagnosis. The fluorescent dye comprises a covalently labeled antibody and is quenched by interaction with an amino acid residue such as tryptophan, tyrosine, histidine, and methionine in the antibody and upon binding of the antibody to an antigen present on a cell surface to emit fluorescence, whereby cells having a target antigen thereon can be imaged for diagnosis. When using the antibody-fluorescent dye conjugate according to the present invention during in vitro cell assays, high-throughput screening of cells, and cytodiagnosis based on microfluidics, the presence of cancer cells having a specific antigen expressed thereon can be detected at high specificity and sensitivity without a washing process, and the position of primary and metastatic cancer cells can be detected at high contrast within a short time.