The purposes of this study were to assess the quality of rainstorm runoffs from an industrial park developed to accommodate general industries in Taiwan and to investigate the possible contributors of pollutants in the runoffs. Rainstorm runoffs from this industrial park were found to contain COD and TSS with average event mean concentrations of two events of 2,202.6 ± 1,356 and 784.7 ± 409 mg/l, respectively. The pollution level of these runoffs was found to be tens of times higher than that which may be contributed by accumulation of pollutants in top soils. Other possible sources of the pollutants were those accumulated in rainwater discharge channels and those which overflow from individual pre-treatment plants within the industrial lots. The assessment results are useful in devising the best management practices for the stormwater discharges. The heavy loadings suggest that installations of additional runoff pollution control practices at different zones are necessary at this and similar industrial parks.