Abstract: A fiber optic attenuation measuring system includesa transmitter for generating and transmitting a reference signal from a first end of fiber optic cable, and a receiver positioned to receive the signal from a second end of the cable. The receiver compares the transmitted signal with a reference signal to determine attenuation through the cable under test. In the preferred embodiment of the invention, the transmitter and receiver are independent units, which may be positioned separately with respect to one another, and the receiver is constructed to enable it to reproduce the reference signal through the use of a timing pulse transmitted with the test signal from the transmitter. In the alternative, a reference cable may link the transmitter and receiver for comparison with the test transmission.