Abstract: A n analyt ical exp ression of the successful guiding p robability of using an ESM senso r guiding a 2D radar is derived fo r a co2located radar2ESM system. W ith the analyt ical exp ression, the successful guiding p robability can be easily obtained. The guiding p robability influenced by an ESM and a 2D radar is studied and four p ropert ies of the successful guiding p robability are p roved. N umerical calculat ion of the successful guiding p robability is conducted fo r several cases and the results verify the p ropert ies of the successful guiding p robability. D iscussions are also made. The conclusions p resented in th is paperw ill be useful in the design of co2located radar2ESM guiding system s. Key words: radar; ESM (Elect ronic Suppo rtM easure) ; guiding; senso r management; data fusion