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Caves are unique environments filled with complex microbial communities that have adapted to oligotrophy. Communities of fungi and bacteria are commonly studied in touristic caves or are associated with guano or other sources of organic matter, but the archaeal community is often overlooked in these conditions. Based on this gap in the existing literature, the present study aims to evaluate the effect of a unique in vitro contamination event by organic matter in the archaeal community over the course of one year. For that purpose, samples were collected in Gruta Manoel Ioio, a limestone cave located in Iraquara, Brazil. The collected samples were transported to the laboratory to undergo an enrichment of 0.25% or 0.5% mixture 1:1 (w/w) of yeast and meat extract. Samplings were collected at 0, 1, 6, and 12 months to evaluate the effects on the archaeal community by polymerase chain reaction followed by Denaturing Gel Gradient Electrophoresis (PCR-DGGE). PCR-DGGE profiles show that Operational Taxonomic Units (OTUs) remained in all samples, but variations were observed among the contaminated and control samples, especially at 6 months. Also, an increase in the number of OTUs was observed in samples that received the addition of organic matter in relation to the control. These OTUs were identified as Euryarchaeota and Crenarchaeota. This study showed that the archaeal community could be impacted by organic matter contamination in caves. [ABSTRACT FROM AUTHOR]