how can you tell if a dog is a chihuahua or a miniature pinscher ?

Answer 1

If the dog has a long tail and the ears are not docked then you would need to either rely on photos suggested in the first answer. A well qualified vet especially one affiliated with the animal shelter in your area can assist in identifying the breed.
In my opinion it shouldn't be too complicated to figure it out on your own. Does this dog look like a small version of a Doberman Pinscher? Long pointed snout, small beady eyes, tight smooth skin with real shiny fur that is slick, ears that either stand straight up or flop down like a hound and the overall look of the body is lean. The tail, if not docked, will point straight out like a hound or retriever's. Then its a Mini Pin.
If it looks a Chihuahua then it will have a shorter snout that can be slightly pointed or boxy, large almost protruding eyes, normal skin flexibility with thicker, longer fur, ears that sit on the head at the 10 and 2 position like a clock face and a fuller stocky body that makes the dog look well-fed. The tail is curled like a sickle and be over the back, sometimes curl to touching the back.
To me the ears are the dead give away even if they have not been cropped to breed standards for a Mini Pin. The Chihuahua's ears sit in a different position entirely than that of the Mini Pin.
The fur as well is very noticeable for breed specifics, look for the slick, very short fur of the Mini Pin.
This should be easy for you base on the breed specifics so get busy.

Answer 2

If you had pictures I could tell you. A chihuahua is smaller, has a smaller head. A min pin has a longer nose, is more muscular. A lot of chihuahuas have the coloring of a min pin. Do you have links to pix that I can see? The link that LuvMyLab posted for chihuahuas is not a good example of the breed.

Answer 3

I go by AKC standards. I look to see the markings on both. I think min pins are easy to tell based on the fact I've been around them all my life. But here's some help:

Miniature Pinscher:
http://www.dogbreedinfo.com/miniaturepinscher.htm

http://www.akc.org/breeds/miniature_pinscher/index.cfm

Chihuahua:
http://www.dogbreedinfo.com/chihuahua.htm

http://www.akc.org/breeds/chihuahua/index.cfm

Min Pin Chihuahua Mix:
http://www.dogbreedinfo.com/chipin.htm

Answer 4

They are very different looking dogs...please post a picture.

The picture that Lovemylab posted actually is not a bad representation of a chihuahua. The dog (and i'm pretty sure it's a male) eyes are a little too small but his head's decent. It's not the over-done, exaggerated head that is currently favored but nonetheless a reasonable specimen (i'm not saying it's a best in show dog)

Answer 5

A Chihuhua has a tail, a Min Pin doesn't.

Answer 6

They look completely different.

Here's a chihuahua:
http://www.chihuahua-pictures.com/images/Yoda100_0067c.jpg

Here's a mini-pin:
http://www.pups4sale.com.au/miniature_pinscher_03a.jpg