Dexmedetomidine is most often used in the intensive care setting for light to moderate sedation. It is not recommended for long-term deep sedation. A unique feature of dexmedetomidine is that it has analgesic properties in addition to its role as a hypnotic, but is opioid sparing; thus, it is not associated with significant respiratory depression. The study is conducted in Anugrah Narayan Magadh Medical College and Hospital in Surgery department. The approval of ethical committee had been taken along with the consent from the patients were also taken. Total 40 patients having are group of 20-60 year were enrolled in to the study. From the present study we conclude that, effect of 6μg Dexmedetomidine Dosage on Duration of Spinal Anaesthesia hydrochloride added to local anaesthetic in subarachnoid block has proved to be a better adjuvant in prolonging the sensory and motor blockade intra-operatively and duration of effective post-operative analgesia compared to 2 μg, without signifcant adverse effects.