diff --git a/backend/app/models/knowledge.py b/backend/app/models/knowledge.py
new file mode 100644
index 0000000..6ed80ef
--- /dev/null
+++ b/backend/app/models/knowledge.py
@@ -0,0 +1,19 @@
+"""Knowledge base document model for RAG."""
+from sqlalchemy import Column, String, Integer, Text, Boolean, ForeignKey
+from app.models.base import Base, TimestampMixin, TenantMixin
+
+
+class KnowledgeDoc(Base, TimestampMixin, TenantMixin):
+    """A document in the project knowledge base for RAG retrieval."""
+    __tablename__ = "knowledge_docs"
+
+    id = Column(Integer, primary_key=True, autoincrement=True)
+    project_id = Column(Integer, ForeignKey("projects.id"), nullable=True)  # null = tenant-level
+    title = Column(String(500), nullable=False)
+    content = Column(Text, default="")
+    doc_type = Column(String(50), default="text")  # text, markdown, url, file
+    source = Column(String(500), default="")
+    tags = Column(String(500), default="")
+    # Simple keyword index for MVP RAG (no vector DB needed)
+    keywords = Column(Text, default="[]")  # JSON array of keywords
+    is_indexed = Column(Boolean, default=True)