For efficient drug delivery, stable encapsulation of a large amount of anticancer drugs is crucial, not to mention cell-specific delivery. Among many possible nanocarriers, mesoporous silica nanoparticles are versatile frameworks that satisfy those requirements owing to their characteristic internal pores with a large surface area and a tunable surface composition. By using a noncovalent post-modification strategy, MSN-based drug delivery systems with enhanced therapeutic efficiency can be prepared in a simple one-pot process by loading small anticancer drugs in the unmodified mesopores and by subsequently blocking the drug-loaded pores with a stimuli-responsive polymer gatekeeper. For targeted delivery, drug-loaded MSNs can be functionalized with suitable targeting components such as targeting ligands or artificial protein corona. This mini-review highlights the recent research in which MSN-supported nanocarriers are designed, synthesized, and characterized to possess a high drug loading capacity and encapsulation stability along with targeting capability for more efficient cancer treatment.