The procedures for determination of circuit breakers reliability indices in Croatian electrical utility are shown. The system for collecting and analyzing failure data is developed. Detailed statistical analysis of collected data on the population of 1224 circuit breaker years is performed. The failure rate of major and minor failures versus exploitation time and nominal voltage are determined. The results are compared with the results of similar surveys of circuit breakers failures in the world. In order to collect accurate data about circuit breaker behaviour the mobile circuit breaker monitoring system was developed, installed and tested for three months in bus coupler bay in transformer substation JARUN in Zagreb. Also the on-line circuit breaker monitoring system is developed and will be installed during 2008 in one bay of transformer substation MELINA near Rijeka. For the purpose of increasing circuit breaker reliability the brand new method for the determination of circuit breaker quality indices is proposed. This method takes in account survey results, diagnostic results, monitoring results as well as results of maintenance. The six circuit breaker quality indices are defined: dielectric state - state of SF6 gas; operation times; voltage drop; switching operations; functional verification and testing; breaking capability. The procedure for determination of circuit breakers quality indices was successfully tested on circuit breaker population in Croatian electrical utility – Transmission operator Zagreb.