In this paper, an evaluation of a product replacement ratio of irreparable items to the normally working ones is performed with a view to a warranty analysis. It is demonstrated that the replacement ratio during the warranty period can be estimated from the field data collected during the period of operation, and one can provide the management with a useful information regarding the appropriateness for the warranty period, which is vital to the product marketing strategy. Although warranty data usually take the form of multiply right censored interval data, the conventional reliability analysis method seems to be good enough as in this case. More sophisticated method such as warranty cost analysis and 2-dimensional warranty analysis is yet desired.