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Due to a lack of effective internal references, studies on functional genes in <i>Phthorimaea operculella</i>, a serious Lepidopteran pest attacking potatoes worldwide, have been greatly limited. To select suitable endogenous controls, ten housekeeping genes of actin (<i>ACT</i>), α-tubulin (<i>α-TUB</i>), glyceraldehyde-3-phosphate dehydrogenase (<i>GAPDH</i>), elongation factor 1α (<i>EF1α</i>), <i>18S</i> and <i>28S</i> ribosomal RNA (<i>18S</i>, <i>28S</i>), ribosomal protein genes <i>RPL4</i>, <i>RPL13</i> and <i>RPL27</i> and superoxide dismutase (<i>SOD</i>) were tested. Their expression levels were determined under three different experimental conditions (developmental stages, tissues/organs and temperatures) using qRT-PCR technology. The stability was evaluated with five methods (Ct value, geNorm, NormFinder, BestKeeper and RefFinder). The results clarified that <i>RPL13</i>, <i>EF1α</i> and <i>RPL27</i> are ranked as the best reference gene combination for measuring gene expression levels among different developing stages and under various temperatures; <i>EF1α</i> and <i>RPL13</i> are recommended to normalize the gene expression levels among diverse tissues. <i>EF1α</i> and <i>RPL13</i> are the best reference genes in all the experimental conditions. To validate the utility of the selected reference pair, <i>EF1α</i> and <i>RPL13</i>, we estimated the tissue-biased expression level of chitin synthase A gene (<i>PoChSA</i>). As expected, <i>PoChSA</i> was abundantly expressed in ectodermally derived epidermal cells, and lowly transcribed in the midgut. These findings will lay the foundation for future research on the molecular physiology and biochemistry of <i>P. operculella</i>.