The effect of the color reaction of magnesium ion with xylidyl blue-1 (XB-1) in the presence of cetyltrimethylammonium bromide (CTMAB),cetylpyridinium bromide (CPB) or Triton X-100 was studied,It was shown that in the presonce of either surfactant mentioned the bathochromic shift of the absorption peak of the roagent blank occurs,whereas the absorption peak of the complex formed from magnesium ion with XB-1 is virtually not effected,thus the contrast of the color reaction is increased.