ZURICH, March 21 (Reuters) - The Swiss National Bank cut its main interest rate by 25 basis points to 1.50% on Thursday, a surprise move which made it the first major central bank to dial back tighter monetary policy aimed at tackling inflation.

It was the first decision since long-serving Chairman Thomas Jordan said he would step down in September.

The decision to cut caught economists by surprise, with a majority of analysts polled by Reuters expecting the SNB to keep rates on hold at 1.75%. It was also the first rate cut by the SNB in nine years. (Reporting by John Revill Editing by Dave Graham)