Despite their great diversity, alkaloids have many common physical and chemical properties. In general, alkaloids are colourless, crystalline (a few are amorphous) with an intensely bitter taste, and have sharp melting points. Alkaloids like nicotine and coniine are liquids and berberine and sanguinarine are coloured. Presence of nitrogen in their structure confers basic properties and they unite with acids to form salts. This facilitates their isolation as water-soluble salts in the presence of mineral acids. Alkaloids are mostly optically active substances.

They are insoluble or sparingly soluble in water. They are soluble in ether, chloroform, and other nonpolar immiscible solvents. Salts of alkaloids formed on reaction of the bases with acids are water soluble, but insoluble in nonpolar solvents. Solubilities of different alkaloids and their salts show considerable variation. N-oxide alkaloids, protoalkaloids, and pseudoalkaloids are water soluble.