Ganoderma lucidum is a medicinal higher Basidiomycetes mushroom that exerts anticancer effects through several different mechanisms. This study investigated the effects of G. lucidum on the telomerase activity and microRNA (miRNA) profiles of MCF-7 cells. According to the cytotoxicity results, the G. lucidum ether extract exhibits the highest cytotoxic potency; therefore it was chosen for the subsequent telomerase activity assay and miRNA profiling. The telomerase activity observed in the cells treated with a half-maximal inhibitory concentration of G. lucidum ether extract (100 µg/mL in dimethyl sulfoxide) was 32.2% lower than that of the control cells treated with 1% dimethyl sulfoxide. Among 1066 miRNAs, the most downregulated miRNA was hsa-miR-27a* (4.469-fold), and the most upregulated miRNA was hsa-miR-1285 (10.462-fold). A database search revealed the predicted miRNAs that target the catalytic subunit of the telomerase enzyme telomerase reverse transcriptase, and only miR-3687 (upregulated 2.153-fold) and miR-1207-5p (upregulated 2.895-fold) were changed by at least 2-fold. The miRNA profile changes demonstrated in this study provide a data set regarding their effects on the pathways that regulate telomerase activity in MCF-7 breast cancer cells treated with G. lucidum. These data should aid the development of novel cancer treatment strategies.