I have black vein on my left side of scrotum is it varicocele?

Varicocele: Varicoceles are tortuous veins around the testicle (mostly on the left side). They are deep inside the scrotum and not usually visible unless they are high grade (grade 3-4). If the vessel is on the surface skin of the scrotum, then that is not a varicocele. A simple physical exam and sometime ultrasound of the testicles can diagnose a varicocele.

Unlikely: Varicoceles are inside the scrotum and are typically not visible. They are usually found by feel and not by appearance. It is possible to have a varicocele and a black vein on your scrotum but many times veins like you are talking about appear without an associated varicocele. If you are concerned that you might have a varicocele, you should see your doctor.