JACKSON, Miss. (AP) _ The first black appointed to Mississippi's Supreme Court says the day he took his oath of office was ''probably the greatest day in my life'' other than his wedding day.

With his wife, Phyllis, by his side, Reuben V. Anderson was sworn in Wednesday by Chief Justice Neville Patterson in a brief ceremony attended by about 100 people.

The 42-year-old Jackson native noted he had come a long way from the young attorney who had to carry his diploma to segregated Mississippi courthouses in the late 1960s as proof of his profession.

After taking the oath, Anderson kissed and hugged his wife. The audience in the court chamber applauded.

Patterson called Anderson's appointment ''a significant occasion.''

Anderson said he enjoyed his eight years a county and circuit court judge, and added, ''I was concerned about making the move, but I am going to enjoy this opportunity just as well.''

Gov. Bill Allain, who made the appointment last Friday, attended the ceremony, but when called upon to speak, quipped, ''I'm a believer in the separation of powers.''

Anderson, in turn, thanked Allain for ''having the confidence in me.''

''If fairness, dedication and hard work will make me successful, I will be,'' Anderson said. ''I thank all of you and I love each one of you, and I won't let you down in this high position.''

Anderson took over for retired Justice Francis S. Bowling of Jackson.

He will serve as an appointed justice until the next statewide election in the fall of 1986, when he can run for the remainder of Bowling's term, which expires in January 1989. If elected in 1986, Anderson said he would run again for a full eight-year term on the nine-member court.

A circuit court judge since 1982, Anderson was chosen from among five candidates recommended to the governor by the Judicial Nominating Committee.

Anderson is a graduate of Tougaloo College and the University of Mississippi School of Law.