Little systematic inquiry has been conducted into the nature and developmental characteristics of children's interests. The purpose of this research was to develop a factored interest inventory for use with children during middle childhood. While there are adult interest inventories, there is at present no accepted children's interest inventory to be used by teachers, parents, counselors, etc. From a review of the literature and from questioning children age 9-13 years, parents of children 9-13 years, and teachers in fourth, fifth, and sixth grade with a Preliminary Children's Interest Inventory (PCII), a large pool of interest items was obtained. These items were used to construct the 121 item Children's Interest Inventory (CII) on which each item was to be checked as Like it very much, Like it some, Don't care one way or the other, Don't like it much, Don't like it at all;The CII was administered to 517 children in grades 4, 5, and 6 in Marshalltown, Iowa. During testing, teachers from each class rated the children on a 1-5 scale as to scholastic, social and creative ability. Children's responses were extremely positive, indicating children like most activities. Items which showed no variability in response were removed before factor analysis;Factor analysis resulted in nine factors for boys and nine factors for girls. Boys' factors in order of variance explained are: Sports, Pretend Play, Science, Creative-Active, People-Home, Religion, Social Awareness, Reading, Verbal. Although factor analysis resulted in nine factors for girls, one factor had only two items loading on it and was not interpretable and was discarded. Girls' factors in order of variance explained are: Pretend Play, Sports, Intellectual, Mechanical, People-Home, Religion, Reading, Creative-Active. Factors found in the study parallel a number of the established factors found in adult interest work. Teacher ability ratings showed little significant relation with children's interest ratings. Several significant sex differences and fewer significant age differences are reported;Items under each of the factors were combined to form the final boys' and girls' form of the Middle Childhood Interest Inventory (MCII).