Aptamers are oligonucleotides selected in vitro by SELEX (Systematic Evolution of Ligands by Exponential Enrichment) which can form a special three-dimensional structure and bind its target with high affinity and specificity. With many advantages over antibodies, such as stability and non-immunogenicity, aptamers show good prospects. However, just a few aptamers have entered clinical trials and only one, pegaptanib, has been approved by FDA for clinical use, because of their insufficient nuclease stability, thermal stability, bioavailability or even affinity. Aptamers need to be optimized to obtain better properties for application. This paper will highlight post-SELEX optimization of present aptamers in recent years. We will clarify four common strategies in detail including truncation, chemical modification, bivalent or multivalent aptamers construction and mutagenesis. A certain aptamer needs to be optimized to improve one or more specific properties according to different application purpose.