Abstract: Objective To detect the expression of HS1-associated protein X-1 （HAX-1） and to investigate its subcellular localization in the peripheral blood mononuclear cells （PBMC） of systemic lupus erythematosus （SLE） patients. Methods Semiquantitative reverse transcriptase polymerase chain reaction （RT-PCR） and Western blot were applied to detect the mRNA and protein expressions of HAX-1 respectively in PBMC of active SLE patients, and subcellular localization of HAX-1 in PBMC was observed by laser scanning confocal fluorescence microscopy. Results Compared with the healthy controls, both the mRNA and protein expression levels of HAX-1 in PBMC were significantly increased in active SLE patients（Z = -2.679, P < 0.01; Z = -4.556, P = 0.000）, and positively correlated with SLE disease activity index （both P < 0.01）. HAX-1 was mainly localized in the mitochondria and endoplasmic reticulum of PBMC. Conclusion HAX-1 may take part in the development of SLE by inhibiting the apoptosis of lymphocytes and inducing the over-activation of them in SLE patients.