Plant extracts, like phytoecdysteroids, are currently studied because of the possibility of their use in plant protection. Phytoecdysteroids are insect steroid hormone analogues, and they are believed to deter invertebrates from plants, either by acting as antifeedants or by being toxic through hormonal disruption on ingestion. We describe here the effects of extract from Spinacia oleracea L. (Chenopodiaceae), a plant producing phytoecdysteroids, on the demographic parameters of Plutella xylostella L. (Lepidoptera: Plutellidae). Spinach is one of the very few crop plants which produce large amounts of phytoecdysteroids. Ecdysteroidal extracts of leaves from this plant were incorporated into food given to third instar larvae for two days. Then the larvae were reared on untreated leaves. The eggs from the emerging adults were picked up for demographic experiments. The rearing of the newly hatched larvae was continued individually on untreated leaves. All experiments were performed on 25 ± 1 ºC, 65 ± 5% RH and a photoperiod of 16:8 (L: D) hours in a growth chamber. Data analysis demonstrated that the fecundity of the females was strongly affected by ecdysteroidal extract. Values of intrinsic rate of increase and net reproduction rate decreased significantly as concentration of the extract increased. However, doubling time increased significantly as concentration of the extract increased. The present study demonstrated that the ecdysteroidal components of the spinach are effective on the demographic parameters of P. xylostella. Therefore, this extract may be potential protectants as botanical alternative agent.