Expectations were for the October reading to come in at 56.1, down from 56.6 in September.
The prices paid index fell to 53.5 from 59.5 last month, more than expectations for that index to fall to 58.0.
The ISM PMI report also comes after the latest US manufacturing PMI from Markit Economics showed manufacturing activity slowing to its lowest since July.
So, overall, a mixed morning for US manufacturing reports.
From ISM, here's a quick snapshot of what some of the survey's respondents had to say this month.
ISM