Nanogels (or nanohydrogels) have been extensively investigated as one of the most promising nanoparticulate biomedical platforms owing to their advantageous properties that combine the characteristics of hydrogel systems with nanoparticles. Among them, smart nanogels that have the ability to respond to external stimuli, such as pH, redox, temperature, enzymes, light, magnetic field and so forth, are most attractive in the area of drug delivery. Besides, numerous multifunctionalized nanogels with high sensitivity and specificity were designed for diagnostic applications. In this feature article, we have reviewed and discussed the recent progress of biodegradable nanogels as smart nanocarriers of anticancer drugs and biomedical diagnostic agents for cancer.