The present invention provides an antibody prepared using a peptide as an antigen, the peptide having 8 to 30 amino acid residues selected from an amino acid sequence at positions 1 to 68 of human high-molecular-weight CD14, or an antibody that binds to a peptide having a specific amino acid sequence at a position among the positions 1 to 68. An assay kit for human low-molecular-weight CD14 using the antibody and an assay method of the present invention, preferably a sandwich method, are able to quantitatively or qualitatively determine human low-molecular-weight CD14 with high sensitivity and specificity in a simple manner, so that they are useful for the diagnosis of a patient suffering from sepsis.