The second law of thermodynamics states that entropy,as a measure of randomness in a system,increases over time.Although previous studies investigated sequence randomness from different aspects,it remains unknown whether sequence randomness changes over time and whether this changes consists with the second law of thermodynamics.In order to fully investigate the dynamics of entropy in molecular sequence evolution,here we propose RDBS(Randomness Detection in Biological Sequence),a tool for detecting sequence randomness based on a collection of eight statistical random tests and examine the randomness of coding sequences with an application to Escherichia coli.