The present study concerns the effectiveness of a selective 5-hydroxytryptamine (5-HT)-1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) in long term sugar diet treated rats. Male albino wistar rats were divided into control and test groups. Test animals were given sugar (5 g/10 ml water) orally for three weeks. Food intakes and body weight of all rats were measured weekly. After three weeks control and test animals were further divided into two groups i.e. saline injected and drug injected. 8-OH-DPAT at a dose of 0.25mg/Kg was injected to a group of normal diet treated and another group of sugar diet treated rats. Other two groups were injected with saline. 5-HT syndrome and food intakes at 2h and 4h were monitored. Then animals were decapitated to collect brain samples for the estimation of 5-HT and 5-hydroxyindole acetic acid (5-HIAA) levels by HPLC-EC method. We observed that weekly cumulative food intakes increased and body weights decreased in sugar diet treated rats. 8-OH-DPAT produced hyperactivity syndrome in both control and sugar treated rats. But these values were smaller in sugar diet than normal diet treated rats. Hyperphagic effects of 8-OH-DPAT were greater in normal diet than sugar diet treated rats. 5-HT and 5-HIAA levels were not altered. The results suggesting a desensitization of pre as well as postsynaptic 5-HT-1A receptors in rats treated with sugar diet are discussed in the context of a role of sugar diet in the precipitation of obesity and other neuropsychiatric illnesses.