The present invention relates to a solid nutrient media composition having alkaline pH, useful for isolating and identifying alkaliphilic microorganisms in pure form. The media composition consists of 5-15 g of carbon source, 2.5-10 g of peptone, 2.5-10 g of yeast extract, 0.5-1.5 g of dipotassium hydrogen phosphate; 0.1-0.5 g of magnesium sulphate heptahydrate, 30 μl-4 ml of super saturated solution of sodium hydroxide, 5-20 g of potassium chloride and 10-30 g of κ-carrageenan in one liter of distilled water. The potassium salt in combination with κ-carrageenan in specific proportion has been found to be a suitable replacement of agar in solidifying bacteriological media especially, for isolation of extreme alkaliphiles. The present invention also provides a method of using the solid nutrient media composition having alkaline pH to study biodiversity of cultivable alkaliphilic bacteria.