IASL(iodo acetamide) and MSL(maleimide) disordered the orderly helix arrangement of myosin in the rest state of spin level. Especially the effect of IASL was great. Equatorial reflection(10,11) change inferred that myosin head was moved to the vicinity of actin filament by spin level. The intensity change of 143Å and 72Å could offer information of the mass projection of population of myosin heads along the filament axis. The slope of intensity profile of the mass projection of 143Å and reflection of IASL is appeared and that of MSL is appeared sharply. The decrease of 215Å reflection intensity is appeared the periodical characteristic of 143Å reflection by spin label. The raise of MSL actin reflection at 51Å and 59Å in the actin reflection change refers that the shifted myosin head binds a certain actin or changes an actin structure by spin label effect. Because iodo acetamide has a tendency to decease the actin reflection, actin close not bind myosin head. From this result, we could conclude that LASL and MSL are spin labeled on SH of myosin head and disordered the helix arrangement of actin.