Bismuth-containing semiconductor material is a hot topic in photocatalysts because of its effective absorption under the visible light. In this paper, we expect to explore a new bismuth-based photocatalyst by studying the subsolidus phase relations of the Bi 2 O 3 -Fe 2 O 3 -La 2 O 3 system. The X-ray diffraction data shows that in this ternary system the ternary compound does not exist, while seven binary compounds (including one solid solution series Bi 1−x La x O 1.5 with 0.167 ≤ x ≤ 0.339) are obtained and eight compatibility triangles are determined.