Aluminum electrolytic capacitors (AEC) as a high energy density, low-cost energy storage component, are widely used in power electronic converters to stabilize the output voltage. However, the AEC is reported as a vulnerable component, threatening the reliability of power electronic converters. The health status of AEC is reflected in the variation of its equivalent series resistance (ESR). Therefore, it is necessary to monitor the ESR of AEC to guarantee the safety and reliability of converters. This paper presents a novel ESR on-line estimation method for both continuous and discontinuous conduction modes of DC-DC boost converter based on output voltage ripple information without using any current sensor. This method is characterized with cost-effective implementation, less computational burden, and acceptable accuracy. In this paper, the calculation model of ESR, online ESR estimation method, and the corresponding hardware implementation are presented. Finally, simulation and experiment results are presented to verify the validity, effectiveness and feasibility of the proposed method in comparison with different estimation methods.