Bolton, a Republican, was nominated by President George Bush three weeks ago amid complaints from Democrats that he is a polarising figure who has shown disdain for the world body.
"We urge you to reject that nomination," the former diplomats said in a letter to Richard Lugar, the chairman of the US Senate Foreign Relations Committee.
The former diplomats, who have served presidents from Richard Nixon to Bill Clinton, took issue with what they said was Bolton's view that the UN is valuable only when it directly serves the interests of the Unites States.
They also said Bolton, currently undersecretary of state for arms control and international security, has an exceptional record of opposing efforts to enhance US security through arms control, and has worked for Taiwan as a paid researcher and has said Taiwan should be treated as a sovereign state.
They said that "his past activities and statements indicate conclusively that he is the wrong man for this position".
US State Department spokeswoman Joanne Moore did not have a comment on the letter.
The Senate panel is set to hold a hearing on Bolton's nomination when Congress returns from its Easter recess in early April.
The letter's signatories include Gerald Helman, former ambassador to the United Nations under president Jimmy Carter; Roger Kirk, former ambassador to Somalia and Romania under Nixon, Gerald Ford and Ronald Reagan, and Princeton Lyman, former US ambassador to South Africa and Nigeria under Reagan, George Bush Sr and Clinton.