Ultrathin single crystal platinum diselenide (PtSe2) nanosheets are synthesized using H2PtCl6 and Se as the precursors. The electronic properties are first investigated and exhibit p-type transport behavior with the mobility much larger than 7 cm(2) V-1 s(-1). The further investigation on PtSe2/MoS2 var der Waals p-n junction demonstrated that PtSe2 could be potentially applied in 2D electronics.