diff -Naur zabbix-3.4.11_origin/include/log.h zabbix-3.4.11_ZBXNEXT-3800/include/log.h
--- zabbix-3.4.11_origin/include/log.h	2018-06-25 11:57:00.000000000 +0300
+++ zabbix-3.4.11_ZBXNEXT-3800/include/log.h	2018-07-02 15:21:35.715692400 +0300
@@ -59,6 +59,9 @@
 #endif
 
 int		zabbix_open_log(int type, int level, const char *filename, char **error);
+int     check_logfile_path(const char *filename);									// ZBXNEXT-3800
+char    *resolve_env_var(const char *filename);										// ZBXNEXT-3800
+
 void		zabbix_errlog(zbx_err_codes_t err, ...);
 void		__zbx_zabbix_log(int level, const char *fmt, ...);
 void		zabbix_close_log(void);
diff -Naur zabbix-3.4.11_origin/src/libs/zbxlog/log.c zabbix-3.4.11_ZBXNEXT-3800/src/libs/zbxlog/log.c
--- zabbix-3.4.11_origin/src/libs/zbxlog/log.c	2018-06-25 11:57:00.000000000 +0300
+++ zabbix-3.4.11_ZBXNEXT-3800/src/libs/zbxlog/log.c	2018-07-02 15:21:55.859692400 +0300
@@ -343,6 +343,37 @@
 	return SUCCEED;
 }
 
+// ZBXNEXT-3800 start
+int check_logfile_path(const char *filename)
+{
+	const char *var_ident = "%";
+	
+	if (strstr(filename, var_ident))
+	{
+		return SUCCEED;
+	}
+	else
+	{
+		return FAIL;
+	}
+}
+
+char *resolve_env_var(const char *filename)
+{
+	char 		*env_name;
+	char 		*env_value;
+	char 		*rest_log_part;
+	const 		char *delimiter = "%";
+	
+	env_name = strtok(filename, delimiter);
+	rest_log_part = strtok(NULL, delimiter);
+	env_value = getenv(env_name);
+	if (env_value != NULL) {
+		return strcat(env_value, rest_log_part);
+	}
+}
+// ZBXNEXT-3800 end
+
 void	zabbix_close_log(void)
 {
 	if (LOG_TYPE_SYSTEM == log_type)
diff -Naur zabbix-3.4.11_origin/src/zabbix_agent/zabbix_agentd.c zabbix-3.4.11_ZBXNEXT-3800/src/zabbix_agent/zabbix_agentd.c
--- zabbix-3.4.11_origin/src/zabbix_agent/zabbix_agentd.c	2018-06-25 11:57:00.000000000 +0300
+++ zabbix-3.4.11_ZBXNEXT-3800/src/zabbix_agent/zabbix_agentd.c	2018-07-02 15:22:11.115692400 +0300
@@ -871,6 +871,7 @@
 	int		i, j = 0;
 #ifdef _WINDOWS
 	DWORD		res;
+	char 		*log_path;
 #endif
 
 	if (0 != (flags & ZBX_TASK_FLAG_FOREGROUND))
@@ -879,12 +880,34 @@
 				CONFIG_HOSTNAME, ZABBIX_VERSION, ZABBIX_REVISION);
 	}
 
+// ZBXNEXT-3800 start
+#ifdef _WINDOWS
+	/* If LogFile contains '%' symbol, if includes Windows environment variable */
+	if (SUCCEED == check_logfile_path(CONFIG_LOG_FILE)) {
+		log_path = resolve_env_var(CONFIG_LOG_FILE);
+		if (log_path == NULL) {
+			zbx_error("cannot resolve environment variable: %s", CONFIG_LOG_FILE);
+			exit(EXIT_FAILURE);
+		}
+	} else {
+		log_path = CONFIG_LOG_FILE;
+	}
+	
+	if (SUCCEED != zabbix_open_log(CONFIG_LOG_TYPE, CONFIG_LOG_LEVEL, log_path, &error))
+	{
+		zbx_error("cannot open log: %s", error);
+		zbx_free(error);
+		exit(EXIT_FAILURE);
+	}
+#else
 	if (SUCCEED != zabbix_open_log(CONFIG_LOG_TYPE, CONFIG_LOG_LEVEL, CONFIG_LOG_FILE, &error))
 	{
 		zbx_error("cannot open log: %s", error);
 		zbx_free(error);
 		exit(EXIT_FAILURE);
 	}
+#endif
+// ZBXNEXT-3800 end
 
 #ifdef HAVE_IPV6
 #	define IPV6_FEATURE_STATUS	"YES"