Results of our NMR measurements of high T-c superconductors are review
ed. From systematic measurements of NQR frequency, Knight shift, nucle
ar spin lattice relaxation rate and nuclear transverse relaxation rate
over a wide hole concentration range from light to heavy doped compou
nds together with the impurity and pressure effect, following results
are concluded. The numbers of the holes at the respective sites of Cu
and O site in the CuO2 plane govern the several physical properties of
the system. There are optimum values of these hole numbers to produce
highest T-c. The superconducting properties are well explained consis
tently by the d-wave pairing model. T-c is found to be correlated inti
mately with the antiferromagnetic spin fluctuation parameters that gov
erns the nuclear relaxation. The mechanism for the superconductivity i
s magnetic in origin.