Unite union members based at plants in Cowley, Goodwood, near Chichester, Hams Hall in the West Midlands and Swindon, turned down the offer by 56.6%.
Workers have already staged four walkouts during the dispute, which is over the closure of a final-salary pension scheme.
BMW said the offer was "fair" and it was disappointed at the ballot result.
Unite representatives will meet on Tuesday to discuss the next steps in the dispute, which has seen the first-ever strikes by the company's British employees.
Three 24-hour strikes scheduled in May were suspended while workers considered the offer, which the union did not recommend to its members.
Unite national officer Fred Hanna said: "It is clear that it did not go far enough or deal with the concerns many of our members have over BMW's pension plans.
"We would urge BMW bosses to reflect on the result and listen to the workforce by further engaging in meaningful talks with Unite."
A BMW spokesman said: "We are now considering the implications of the ballot result and we will be meeting with the union in due course to discuss next steps.
"We believe the offer, which resulted from lengthy negotiations with the union since September last year, was fair.
"It was designed to improve competitiveness, which is in the long-term interests of all our employees in the future."
Workers at car giant BMW have voted to reject an offer aimed at resolving a long-running dispute over pensions.