Epigenetic alterations are strongly associated with cancer development and drug resistance. The use of the DNA methylation inhibitor decitabine (Dacogen®) has been approved in the treatment of hematological malignancies, and its clinical effects on solid tumors have gained attention. Here, we present a review of the molecular regulation mechanisms, clinical experiences and biological evaluation for novel decitabine-based therapies in solid tumors. We also discuss the following questions: What is the best administration schedule of decitabine in solid tumors? Is there tumor type specificity for decitabine-based epigenetic therapy? What are the biological function and mechanism of decitabine in suppressing tumor development? Is there a correlation between DNA demethylation and clinical response? Importantly, low-dose decitabine and combined therapy show significant improvement in solid tumor treatment. However, the correlation studies are preliminary, and key biomarkers for prognosis need further investigation.