According to the 28 Apr 1965 Var, writer Robert L. Joseph was initially hired to adapt the Rohan O’Grady’s 1963 novel to the screen. He was later replaced by Mark Rodgers. On 21 Jun 1965, DV mentioned comic actor Al Lewis as a possible cast member. Casting was still underway five weeks later, when the 28 Jul 1965 Var noted that the producers were seeking several “smaller children, an English boy and an American or Canadian girl.” Principal photography began 20 Dec 1965, as stated in the 29 Dec 1965 Var. The 22 Dec 1965 LAT claimed that actor Leslie Nielsen might appear in the film, after scheduling around his current project, Beau Geste (1966, see entry). The 10 Jan 1966 DV included assistant directors Terry Morse, Jr., James C. Welch, and Wendell Franklin among the crew. A news item in the 1 Sep 1966 Los Angeles Sentinel stated that special-effects man Roland “Punky” Chiniquy sheathed the stinger of a tarantula with adhesive tape to protect actor Nigel Green.
       A news brief in the 14 Feb 1966 DV indicated that editing was currently in process. The 15 Jul 1966 DV and 20 Jul 1966 Var noted that Marvin Miller voiced five radio advertisements for the film, and narrated the theatrical trailer.
       Let’s Kill Uncle opened 12 Oct 1966 in Los Angeles, CA, and on 18 Nov 1966 in New York City to mixed reviews. While the 21 Sep 1966 Var considered it the ideal picture for its adolescent target audience, the 19 Nov 1966 NYT suggested it would have been much better with a more capable director. A Detroit, MI, opening preceded in late Sep 1966, according to the 28 Sep 1966 Var. The picture closed in Providence, RI, during mid-Apr 1967, as indicated by 19 Apr 1967 box office reports.
       An obituary in the 24 Mar 2007 NYT noted that Let’s Kill Uncle marked the final film score of composer Herman Stein.