RNAi-based gene-silencing techniques offer a fast and cost-effective way of knocking down genes' functions in an easily regulated manner. Exciting progress has been made in recent years in the application of these techniques in basic biomedical research and therapeutic development. However, it remains a difficult task to design effective siRNA experiments with high efficacy and specificity. We present siRecords, an extensive database of mammalian RNAi experiments with consistent efficacy ratings. This database serves two purposes. First, it provides a large and diverse dataset of siRNA experiments. This dataset faithfully represents the general, diverse RNAi experimental practice, and allows more reliable siRNA design tools to be developed with the overfitting problem well curbed. Second, the database helps experimental RNAi researchers directly by providing them with the efficacy and other information about the siRNAs experiments designed and conducted previously against the genes of their interest. The current release of siRecords contains the records of 17,192 RNAi experiments targeting 5086 genes.