Art therapy assumes that art work is related to differential constructs of the artist. Empirically, this hypothesis has not been proven yet because quantitative methods are rare. The Rating Instrument for two-dimensional Pictorial Work (RizbA) is designed to address this issue. The construct – pictorial expression – is theoretically defined by seven content areas (representation, color, shape, space, motion, composition, expression), which combined create the overall construct. Test development is based on art historical and art therapeutic theories and supported empirically. Two online studies are conducted using a sample of nine pictures, which are rated by experts (n1 = 12, n2 = 8). In the first study, based on psychometric characteristics, an item pool of 113 items is examined and a preliminary test version is developed. The second study examines quality criteria of the preliminary version. For both studies, factor analyses are computed. The preliminary version includes 26 items. Its ability for differentiation between pictorial works ranges between .897 (T1) and .766 (T2), its inter-rater reliability between .525 (T1) and .917 (T2). Test-retest reliability is .919. PCA suggests a four-factors solution, which in large part is consistent across studies. As a reliable measurement RizbA opens new perspectives in fundamental art therapeutic and psychological research.