The present disclosure concerns aptamers of formula (I) capable ofspecifically binding toFactor Xla. The aptamers can be used to prevent, treat or alleviate thesymptoms ofthrombosis. The aptamers can also be used to detect Factor Xla in a sampleand/or purifyFactor Xla from a sample. The aptamers can further be used to identityputative therapeuticagents for the prevention, treatment or alleviation of symptoms associatedwith thrombosis.