We synthesized a series of novel pyrazolyl hydroxamic acid derivatives (4a–4l) and investigated their biological activitiesagainsthumanlung cancer celllineA549 in vitro to determine their mechanism of action. The results showed that the majority of derivatives had inhibitory effects on the growth of A549 cancer cells in dose and time-dependent manners, in which the compounds 4b, 4f, 4h and 4j