In a strong field, Muir clocked 4:11.48 to finish behind world record holder Genzebe Dibaba, Commonwealth champion Faith Kipyegon, European champion Sifan Hassan and Ethiopia's Dawit Seyaum.
"I'm really pleased. That was such a tough field," said the Scot, 22.
"I think any other year I probably would have medalled."
Muir added: "I expected it to be hard - it's a championship final.
"There are so many girls in there, you don't know who is going to do what but I was prepared for a fast race or a slow race and I just worked on staying out of trouble.
"This is the first time I've done three rounds, so to have got three and done them well, my preparation for [the Rio Olympics] next year is good."
Muir - who was three seconds behind Ethiopian winner Dibaba - said she was pleased to have posted a good time in Beijing after missing out on the 800m final at last year's World Indoor Championships and not picking up a medal at the Glasgow 2014 Commonwealth Games.
"I left last year so frustrated as I knew I could run so much better but it's great to have come here and have done well in the final," she added.
Britain's Laura Muir said she was delighted with her fifth place in the 1500m final at the World Athletics Championships in Beijing.