Proton beam extinction, defined as a residual to primary ratio of beam intensity, is one of the most important parameters to realize the future muon electron conversion experiment (COMET) proposed at J-PARC. To achieve the required extinction level of 10-9, we started measuring extinction at main ring (MR) as its first step. According to the various measurements done at the different positions, empty RF buckets of RCS, which were considered to be swept away by the RF chopper, contained about 10-7 ∼10 -5 of the main beam pulse due to chopper inefficiency. We have developed a new beam monitor with improved performance for further studies at the abort line. In addition, we have started new measurements at the Hadron experimental hall by using slow-extracted beam. In this paper, we present recent results and future prospect of beam extinction measurements.