diff --git a/relay/channel/ali/adaptor.go b/relay/channel/ali/adaptor.go
index cb3070ff367..96f91f48ed8 100644
--- a/relay/channel/ali/adaptor.go
+++ b/relay/channel/ali/adaptor.go
@@ -11,6 +11,7 @@ import (
 	"github.com/QuantumNous/new-api/dto"
 	"github.com/QuantumNous/new-api/relay/channel"
 	"github.com/QuantumNous/new-api/relay/channel/claude"
+	"github.com/QuantumNous/new-api/relay/channel/deepseek"
 	"github.com/QuantumNous/new-api/relay/channel/openai"
 	relaycommon "github.com/QuantumNous/new-api/relay/common"
 	"github.com/QuantumNous/new-api/relay/constant"
@@ -72,6 +73,7 @@ func (a *Adaptor) ConvertGeminiRequest(*gin.Context, *relaycommon.RelayInfo, *dt
 
 func (a *Adaptor) ConvertClaudeRequest(c *gin.Context, info *relaycommon.RelayInfo, req *dto.ClaudeRequest) (any, error) {
 	if supportsAliAnthropicMessages(info.UpstreamModelName) {
+		deepseek.EnsureThinkingBeforeToolUse(req)
 		return req, nil
 	}
 
diff --git a/relay/channel/deepseek/adaptor.go b/relay/channel/deepseek/adaptor.go
index 60eaf22be56..1bccf7d4dee 100644
--- a/relay/channel/deepseek/adaptor.go
+++ b/relay/channel/deepseek/adaptor.go
@@ -40,6 +40,8 @@ func (a *Adaptor) ConvertClaudeRequest(c *gin.Context, info *relaycommon.RelayIn
 	if err := applyDeepSeekV4ClaudeThinkingSuffix(info, claudeRequest); err != nil {
 		return nil, err
 	}
+	// DeepSeek V4 requires thinking blocks before tool_use when thinking is enabled
+	EnsureThinkingBeforeToolUse(claudeRequest)
 	return claudeRequest, nil
 }
 
diff --git a/relay/channel/deepseek/thinking.go b/relay/channel/deepseek/thinking.go
new file mode 100644
index 00000000000..c981411479d
--- /dev/null
+++ b/relay/channel/deepseek/thinking.go
@@ -0,0 +1,77 @@
+package deepseek
+
+import (
+	"strings"
+
+	"github.com/QuantumNous/new-api/dto"
+)
+
+// EnsureThinkingBeforeToolUse ensures that when thinking mode is enabled,
+// every tool_use block in assistant messages has a preceding thinking block.
+// DeepSeek V4 requires thinking blocks before tool_use when thinking is enabled.
+func EnsureThinkingBeforeToolUse(req *dto.ClaudeRequest) {
+	if req == nil || len(req.Messages) == 0 {
+		return
+	}
+	// Only process deepseek-v4-* models
+	if !isDeepSeekV4(req.Model) {
+		return
+	}
+	// Thinking disabled? skip
+	if req.Thinking != nil && req.Thinking.Type == "disabled" {
+		return
+	}
+	for i := range req.Messages {
+		msg := &req.Messages[i]
+		if msg.Role != "assistant" {
+			continue
+		}
+		contentList, ok := msg.Content.([]any)
+		if !ok || len(contentList) == 0 {
+			continue
+		}
+		contentList, fixed := ensureThinkingInContentArray(contentList)
+		if fixed {
+			msg.Content = contentList
+		}
+	}
+}
+
+// isDeepSeekV4 checks if the model name belongs to DeepSeek V4 series.
+func isDeepSeekV4(modelName string) bool {
+	return strings.HasPrefix(modelName, "deepseek-v4-")
+}
+
+// ensureThinkingInContentArray inserts an empty thinking block at position 0
+// if the content array contains any tool_use without a thinking block as the first element.
+// Returns the modified slice and whether modifications were made.
+func ensureThinkingInContentArray(contentList []any) ([]any, bool) {
+	if len(contentList) == 0 {
+		return contentList, false
+	}
+	// Check if the first element is already a thinking block
+	if first, ok := contentList[0].(map[string]any); ok && first["type"] == "thinking" {
+		return contentList, false
+	}
+	// Check if there are any tool_use blocks
+	hasToolUse := false
+	for _, item := range contentList {
+		if m, ok := item.(map[string]any); ok && m["type"] == "tool_use" {
+			hasToolUse = true
+			break
+		}
+	}
+	if !hasToolUse {
+		return contentList, false
+	}
+	// Insert empty thinking block at the beginning
+	emptyStr := ""
+	thinkingBlock := map[string]any{
+		"type":     "thinking",
+		"thinking": emptyStr,
+	}
+	contentList = append(contentList, nil)
+	copy(contentList[1:], contentList[0:])
+	contentList[0] = thinkingBlock
+	return contentList, true
+}