Municipal solid waste incineration bottom ash (IBA) shows large heterogeneity because of different garbage composition, incineration process and storage conditions. The effective cooperation for one batch of recycled concrete (mortar) may be ineffective for another batch, resulting in large dispersion of recycled concrete (mortar) performance, which limits its application. In order to explore the heterogeneity of IBA from different sources and the strength variability of recycled mortar, this study collected a total of 14 batches of IBA samples from different incinerators and different monthly sources and tested for their physical and chemical properties. And it investigated the workability, compressive strength, and splitting tensile strength of IBA recycled mortar. Statistical analysis was conducted to assess the level of strength variability in IBA recycled mortar. The test results showed that the crushing index, porosity, sulfide, and chloride content of IBA did not meet the specifications for recycled fine aggregates, and there is significant heterogeneity in IBA from different origins. When the recycled cement mortar below M20 strength grade is prepared with a substitution rate of 50% IBA which is from a single incineration plant of different months, the strength is not significantly reduced compared with that of natural aggregate mortar, and the strength variability is similar to that of ordinary recycled aggregate concrete and the standard deviation is also lower than the recommended value of the specification. However, when used to prepare the recycled cement mortar above M20, the reduction in compressive strength was significant (reduced by 23%～32%). Due to higher compressive strength variability of IBA recycled mortars from two different incineration plants, it was not recommended to use IBA recycled mortars from different incineration plants together.