In this account,a rapid retrosynthesis-based scoring method for the assessment of synthetic accessibility of drug-like molecules,called RASA(Retrosynthesis-based Assessment of Synthetic Accessibility) is devised.RASA firstly constructs a synthesis tree for the target molecule based on retrosynthetic analysis;in this process a series of strategies are suggested for limiting combinatorial explosion of the synthesis tree.A scoring function (RASA-score) for the assessment of synthetic accessibility is then proposed based on the optional effective synthetic routes,the complexity of reaction and the difficulty of separation/purification associated with the most favorable synthetic route.