Nobel Prize of medicine and physiology has granted to detector scientists of biological clock in 2017 which shows the importance of this phenomenon in life of creations. All organisms like humans possess an inner biological clock which helps them in adaptation with regular rhythms of day and night. Circadian rhythms of human are inner rhythms with stretch about 24 hours which are directed by environment signs like lightness/darkness cycle. The main part of clock harmony of body circadian is located in suprachiasmatic nucleus (SCN) in hypothalamus. Circadian clock system adjust many biological activities of humans. Recent advanced research, has drastically showed the role of genetic factors in circadian rhythmic system. The relationship between disorder in circadian rhythm and its genes has been reported with a many human diseases. Here, a brief explanation of relationship of this system with sleep disorder diseases, autism spectrum disorder (ASD) and different kinds of cancers in human is represented.