The proportion of GCSEs awarded at least a C grade this summer fell 1.3%, marking the biggest fall in the exam's 25-year history.
Official figures showed entrants scoring A*-C dropped for the second year running to 68.1%.
Those achieving an A* also fell by 0.5%, with 6.8% awarded the top GCSE grade.
ITV News correspondent Damon Green reports:
The overall GCSE A*-G pass rate also fell slightly this year to 98.8%, compared to 99% last year.
The fall comes amid major upheaval in the exam system, including:
A rise in the number of pupils entering maths GCSE early or multiple times
A revamp in science GCSEs after a 2009 report said they were too easy
An increase in the number of pupils taking international GCSEs (IGCSE)
Girls continued to out-perform boys, scoring higher results at A* and A*-C across all subjects.
The general secretary of the National Union of Teachers, the largest teachers’ union, blamed the "obsessive target driven culture" in schools for "stifling learning".
After congratulating pupils on their results, Christine Blower added, “Schools and pupils are being put under ridiculous pressures to meet the latest demands from Ofsted and the Government."
The Department for Education wrote on Twitter:
Education Minister Elizabeth Truss said, "It is very pleasing to see the increase in these important subjects – the ones that will keep pupils’ options open in the future."