Micro(nano)plastics (MNPs), as a globally emerging environmental pollutant, are now ubiquitous in natural environments and can continuously enter the human body through ingestion, inhalation, and dermal contact. This widespread exposure has raised significant concerns regarding the potential health risks posed by MNPs. Although epidemiological studies are still in the early stages, accumulating in vitro cellular experiments have provided key evidence suggesting that nano- to micro-sized plastic particles can cross physiological barriers in the human body. These particles enter cells via endocytosis or direct penetration through the cell membrane, triggering toxic effects such as oxidative stress, immune responses, mitochondrial dysfunction, and DNA damage, which can potentially lead to cell apoptosis. These findings highlight that the direct interaction between MNPs and human cells could be a core mechanism underlying their potential health hazards. This review systematically summarizes the toxic effects of MNPs exposure on various human cell types, exploring the underlying molecular mechanisms and providing insights for future research into the toxicological impacts of MNPs and their implications for human health risk assessment.