The visit, hours after Russia held talks on Ukraine with the United States, is likely to anger Kiev and the West, which accuse president Vladimir Putin of illegally seizing the Black Sea peninsula after a March 16 referendum they say was a sham.
Shortly after landing in Crimea's main city of Simferopol with many members of his cabinet, Medvedev chaired a Russian government meeting attended by Crimean leaders and outlined moves to revive the region's struggling economy.
"Our aim is to make the peninsula as attractive as possible to investors, so that it can generate sufficient income for its own development. There are opportunities for this - we have taken everything into consideration," he told the televised meeting, sitting at a large desk with Russian flags behind him, Reuters reported.
"And so we have decided to create a special economic zone here. This will allow for the use of special tax and customs regimes in Crimea, and also minimize administrative procedures."
In comments that made clear Russia had no plans to give back Crimea, he set out moves to increase wages for some 140,000 state workers in Crimea, boost pensions, turn the region into a tourism hub, protect energy links with the peninsula and improve its roads, railways and airports.
Russia's swift takeover of Crimea, following the ouster of Moscow ally Viktor Yanukovich as Ukraine's president in late February, has caused the biggest crisis in East-West relations since the Cold War.
Medvedev's visit underlined the impotence of the West and Ukraine to force Russia out following the formal annexation of Crimea, signed by Putin, on March 21.
Medvedev arrived in Simferopol hours after US Secretary of State John Kerry met Russian Foreign Minister Sergei Lavrov in Paris late on Sunday and reiterated that Washington considered Russia's actions in Crimea "illegal and illegitimate".