Ankylosing spondylitis (AS) is an inflammatory rheumatic disease. Phlegmasia cerulea dolens is a severe form of deep vein thrombosis characterized by swelling, pain, and bluish discoloration. Treatment delay may cause venous gangrene, tissue ischemia, limb loss or death. Here, we present an AS case who presented with phlegmasia cerulea dolens and treated by catheter-directed thrombolysis.