Objective To explore the differential diagnosis between skeletal fluorosis and ankylosing spondylitis. Methods 62 patients of skeletal fluorosis provided by a specialized hospital in Shanxi province and 54 AS patients admitted to Shanxi Provincial Corps Hospital from August 2009 to March 2010 were retrospectively analyzed. Results The age of onset（42.9±6.66） and number of peripheral joint pain (≥3)in skeletal fluorosis group were above those in AS group, and the difference was statistically significant（P <0.01）. The  rate of  deterioration after exercise( 83.9%,52 cases）was higher than that in AS group( 5.56%, 3 cases)（P<0.01）. The positive rate of HLA-B27 in skeletal fluorosis group  (3.2% , 2 cases)  was lower than that in AS group( 90.7% ,49 cases)（P<0.01）. The rate of limb bone lesions  (100%, 62 cases) , peripheral  joint  disease（90.3%, 56cases）  and interosseous membrane calcification（27.4%, 17 cases）was higher than in AS group（P<0.01）. The rate of spinal slub amyloidosis（61.3%, 38 cases）was higher than that in AS group (22.2%, 12cases)（P<0.05）. The rate of bone destruction in skeletal fluorosis group（0%,0 cases）was lower than that in AS group(29.6%,16 cases) (P<0.01).  Conclusions Correct diagnosis should be made based on epidemiology、clinical manifestations、HLA-B27 test and imaging manifestations   between skeletal  fluorosis  and ankylosing  spondylitis.