Background: As one of the most common intracranial tumors, pituitary adenomas, especially the Cushing's disease subtype, have been studied for many years. However, at present, effective methods for the early diagnosis of pituitary adenomas are very limited, especially for subtypes such as Cushing's disease. Therefore, it is of urgent importance to find effective molecular targets to develop new diagnostic and therapeutic methods for pituitary adenomas. Methods: We showed the abnormally high expression of miR-30d in pituitary adenomas by analyzing data in the Gene Expression Omnibus (GEO) database and revealed a novel molecular mechanism of miR-30d in regulating the proliferation and invasion of a pituitary adenoma cell line (AtT-20). Cell culture and transfection, and RNA interference (RNAi) were used to treat AtT-20 cells to test the effects of miR-30d and TIMP3 on cells. Quantitative polymerase chain reaction (qPCR) was used to determine the messenger RNA (mRNA) expressions. We used 3-(4,5-diphenyltetrazolium bromide) (MTT) to determine cell viabilities. An invasion assay was performed using Transwell chambers. Luciferase activity was tested with a dual-luciferase assay. Results: We found that the expression of miR-30d in pituitary adenoma was higher than that in normal pituitary tissues. It was revealed that miR-30d promoted the proliferation and invasion of AtT-20 cells by inhibiting the expression of TIMP3. In the above process, miR-30d could bind to the 3'-untranslated region (3'-UTR) of TIMP3 mRNA. Conclusions: The mir-30d/TIMP3 signaling pathway plays an important regulatory role in pituitary adenomas. These new discoveries may reveal more functions of miR-30d and lay the foundation for future clinical development of new drug targets.