does any one know why helium gas makes your voice sound funny?????

that helium changes your voice by altering the vibration of your vocal cords. This does have an effect, but it's not as important as the shift in the resonant frequencies of your vocal tract.

it changes the frequency of our voice.so it will make our voice funny.but it is toxic to inhale helium.

When you talk, air travels from your lungs up through the larynx and out of your mouth. The larynx has a pair of vocal folds which form a V-shaped slit. When the air is leaving, it hits the underside of the vocal folds and makes them vibrate. This vibrating excites air molecules in your vocal tract. By moving your tongue, lips, roof of your mouth, etc. you can create recognisable sounds. So that is how sound works. Helium is much lighter than air. Because of this, the speed of sound is much higher in helium. As the sound waves move through the helium, they move more quickly than they do in air. When you inhale helium you increase the speed of the sound of your voice. The shape of your vocal tract does not change. If you increase the speed of a sound you also increase the wavelength. However, on the way to the ear the sound travels through air again and the wavelength goes back to normal. It is not the change in frequency that gives you the squeaky voice but a change in pitch. The sound has the same frequencies but helium causes a shift in your timbre. This means the higher frequencies are getting a higher enhancement than normal so the pitch changes. Although this does not change the frequency of the sound wave, it does enhance the higher frequencies of your voice. This emphasis on the higher frequencies is heard as a higher pitch. If the gas in your voice box had heavier molecules than air, the opposite would occur. The sound produced by your voice would seem lower. No one will disagree that helium changes your voice, but not everyone believes it is helium that causes your voice to become high-pitched. What it does is change the timbre of your voice. (Timbre is what allows you to tell the difference between the same note played at the same volume on two different instruments. It also helps you hear the different parts of speech, like vowel sounds.) The end result? You sound like Donald Duck or a chipmunk. The funny voice that results gives everyone a laugh. Your voice may sound "funny," but it is not worth the risk. Doctors around the world are concerned about the health risk associated with people inhaling helium. However, members of the public have not yet realised the extreme danger associated with helium inhalation.