In this study, we examined the effects of Pleurotus nebrodensis on systolic blood pressure of spontaneously hypertensive rats. Single-dose and continuous-dose tests with sample diets made from the fruit body of the mushroom, P. nebrodensis were carried out on SHR and control rats. Sample diets included 6% dry powder of fruit body (6% dry powder), hot water extract, polysaccharide fraction, protein fraction, dialyzable fraction and non-dialyzable fraction. Polysaccharide and protein fractions were obtained by hot water extraction. The protein fraction was separated to the dialyzable fraction and non-dialyzable fraction by dialysis. In the single-dose test, protein fraction, hot water extract and polysaccharide fraction decreased systolic blood pressure. Blood pressure was lowered after administration for 2 h, and it returned to the pre-administration blood pressure after 48 h. In the continuous-dose test, spontaneously hypertensive rats were fed each of the diets for 16 weeks. The 6% dry powder group showed significantly inhibited elevation of blood pressure compared with the control group and there was no influence on total cholesterol and triglyceride levels. The non-dialyzable fraction showed suppression of increase in blood pressure from the start of the continuous oral administration. Effects on the rennin angiotensin system and renal function were also indicated. The antihypertensive action effect of P. nebrodensis can be expected to not only prevent but also to improve hypertension.