We employed an <i>in vivo</i> assay system of <i>Caenorhabditis elegans</i> to determine if and which microRNAs (miRNAs) were dysregulated upon exposure to coal combustion related fine particulate matter (PM<sub>2.5</sub>) by profiling the miRNAs using SOLiD sequencing. From this, expression of 25 miRNAs was discovered to become dysregulated by exposure to PM<sub>2.5</sub>. Using the corresponding <i>C. elegans</i> deletion mutants, 5 miRNAs (<i>
mir-231</i>, <i>
mir-232</i>, <i>
mir-230</i>, <i>
mir-251</i> and <i>
mir-35</i>) were found to be involved in the control of PM<sub>2.5</sub> toxicity. Furthermore, mutation of <i>
mir-231</i> or <i>
mir-232</i> induced a resistance to PM<sub>2.5</sub> toxicity, whereas mutation of <i>
mir-230</i>, <i>
mir-251</i>, or <i>
mir-35</i> induced a susceptibility to PM<sub>2.5</sub> toxicity. SMK-1, an ortholog of the mammalian SMEK protein, was identified as a molecular target for <i>
mir-231</i> in the regulation of PM<sub>2.5</sub> toxicity. In addition, the genes of <i>
sod-3</i>, <i>
sod-4</i> and <i>
ctl-3</i>, which are necessary for protection against oxidative stress, were determined to be important downstream targets of <i>
smk-1</i> in the regulation of PM<sub>2.5</sub> toxicity. The triggering of this <i>
mir-231</i>-SMK-1-SOD-3/SOD-4/CTL-3 signaling pathway may be a critical molecular basis for the role of oxidative stress in the induction of coal combustion related PM<sub>2.5</sub> toxicity.