The International Paralympic Committee (IPC) only had to ban one federation -- the Paralympic Committee of Russia -- while the IOC had to take a decision involving competitors from 28 international federations, Bach told Reuters in an interview.
The IOC refused to impose a blanket ban on Russia following revelations of state-backed doping across all sports and instead set criteria for Russian competitors, including a clean doping past and sufficient international tests, to be eligible for Rio.
A report commissioned by the World Anti-Doping Agency also found widespread violations at the 2014 winter Olympics in Russia's Sochi, with positive tests replaced by clean samples from Russian competitors.
"It is a different situation and therefore a different decision," Bach said. "The IPC has just only one member federation in Russia.
"This you can compare for instance with the situation in the International Weightlifting Federation where also the IOC accepted and helped and supported the decision to exclude the whole team because you had so many cases."
Russian weightlifters were banned from the Games by the international federation while the country's track and field team has also been essentially excluded with only one Russian track and field athlete competing in Rio.
DIFFERENT SITUATIONS
"I think it is exactly this fact of the very different situations that Phil Craven, the chair of the IPC, supported in his capacity as a member of the IOC, the IOC decision," Bach said.
"But then had a different decision in a different situation (for his organisation)."
The IOC was criticised for not excluding Russia, though more than 100 competitors from the country's original team will not be in Rio, with Russia represented by 278 sportspeople in total.
Several national anti-doping bodies (NADOs), including Germany's, had wanted a blanket ban on Russia.
The head of the German and Austrian anti-doping bodies on Monday called for a ban on Russia for the 2018 winter Olympics in Pyeongchang over the Sochi 2014 doping revelations.
"That's one of our demands," said Andrea Gotzmann. "Just like the fact that we wanted to ban the Russians from the summer Olympics, but here (the winter Games) it is even worse and more detailed because we saw this manipulation in the laboratory in Sochi.
"It is adventurous what went on there. Here there was a criminal energy being used to undermine the system and I think that it cannot be any worse."
(Reporting by Karolos Grohmann; Editing by Ken Ferris)
