Polonium is a chemical element; it has symbol Po and atomic number 84. A rare and highly radioactive metal with no stable isotopes, polonium is a chalcogen and chemically similar to selenium and tellurium, though its metallic character resembles that of its horizontal neighbors in the periodic table: thallium, lead, and bismuth. Due to the short half-life of all its isotopes, its natural occurrence is limited to tiny traces of the fleeting polonium-210 in uranium ores, as it is the penultimate daughter of natural uranium-238. Though longer-lived isotopes exist, such as the 124 years half-life of polonium-209, they are much more difficult to produce. Today, polonium is usually produced in milligram quantities by the neutron irradiation of bismuth. Due to its intense radioactivity, which results in the radiolysis of chemical bonds and radioactive self-heating, its chemistry has mostly been investigated on the trace scale only.

पोलोनियम एक रासायनिक तत्व है। इसकी खोज सन् १८९८ में मेरी क्युरी और प्येर क्युरी ने की थी। यह एक रेडियोएक्टिव तत्व है जिसके मुख्य समस्थानिक का द्रव्यमान २१० है,लेकिन इसके अलावा पोलेनियाम के १० अन्य समस्थानिक ज्ञात है जो आवर्त सारणी में किसी तत्व के सर्वाधिक समस्थानिक है