Our objective in this study is to assess the safety of docosahexaenoic acid (DHA) fortified milk of dairy cows fed feeds containing protected fish oil treated with formaldehyde by analyzing formaldehyde concentration in commercial milk and DHA fortified milk of dairy cows fed formaldehyde treated feed. There are 3 milk samples in this study: Commercial milk (CM), DHA fortified milk for Kid (DHA-K) and DHA fortified milk for Baby (DHA-B). We confirm the fresh quality of these three samples by physicochemical tests. In fat content result, three groups are significantly different at the p < 0.05 by Duncan's multiple range test, but fat content of group DHA-K is about half the level of the other two groups. Protein content of group DHA-K is 1% higher than other two groups. According to the analysis result of DHA content of DHA fortified milk, DHA content of DHA-B is two-fold higher than DHA-K. Similar pattern was seen in the intake based on age. According to HPLC analysis result of formaldehyde concentration in milk, commercial milk and DHA fortified milk are between 0.013 ppm and 0.057 ppm which is formaldehyde standard level in fresh milk settled in WHO (World Health Organization). Three groups have no significantly differences at the p < 0.05 by Duncan’s multiple range test. For this reason, it can be concluded that there is no transition of formaldehyde from dairy cows fed formaldehyde treated feeds to its produced milk. Safety about formaldehyde of DHA fortified milk of dairy cows fed formaldehyde treated feeds is considered similar to commercial milk.